Abstract:
A bearing arrangement for a turbocharger, including a bearing housing-which extends in an axial direction, an anti-friction bearing, situated within the bearing housing, having an outer bearing ring and a number of rolling bodies and an axially extending shaft which is rotatably mounted within the bearing housing. It is provided that the shaft includes a rolling body raceway for guiding the rolling bodies. Moreover, the invention relates to a turbocharger having such a bearing arrangement. A bearing arrangement of this type allows the secure mounting of a shaft in a turbocharger with simple assembly and low costs.

Description:
[0001]    The present invention relates to a bearing arrangement for a turbocharger, including a bearing housing, an anti-friction bearing, situated within the bearing housing, having an outer bearing ring and a number of rolling bodies, and an axially extending shaft which is rotatably mounted within the bearing housing. 
         [0002]    Moreover, the present invention relates to a turbocharger having an above-mentioned bearing arrangement. 
       BACKGROUND 
       [0003]    A turbocharger is usually used for increasing the power of internal combustion engines by utilizing exhaust gas energy. For this purpose, the turbocharger is composed of a compressor and a turbine which are connected to one another via a shaft mounted within a bearing housing. 
         [0004]    During operation, the turbine is set into rotation by an exhaust gas flow, and via the shaft drives the compressor, which draws in and compresses air. The compressed air is led into the engine, a large quantity of air entering into the cylinders during the induction stroke due to the increased pressure. As a result, the oxygen content required for the combustion of fuel correspondingly increases, so that more oxygen enters into the combustion chamber of the engine with each intake stroke. 
         [0005]    This results in an increase in the maximum torque, causing the power output, i.e., the maximum power at a constant working volume, to increase. This increase allows in particular the use of a more powerful engine having approximately the same dimensions, or alternatively, allows a reduction in the engine dimensions, i.e., achieving comparable power with smaller and lighter machines. 
         [0006]    Since the shaft rotates at a high rotational speed during operation of a turbocharger, the shaft must be securely mounted to allow problem-free operation of the turbocharger. 
         [0007]    A bearing unit, designed as a bearing mounting system, for a turbocharger of the type mentioned at the outset is known from DE 689 08 244 T2. A shaft is situated within a bearing housing. The bearing of the shaft within the bearing housing occurs via a pair of anti-friction bearings designed as ball bearings. The ball bearings in each case are composed of an outer bearing ring and an inner bearing ring, the inner bearing rings being fixedly fastened to the shaft. 
       SUMMARY OF THE INVENTION 
       [0008]    Due to the above-mentioned configuration, a shaft of a turbocharger may be securely mounted, even at increased rotational speeds of the shaft. However, the use of a plurality of required separate bearing components and the associated high assembly cost do not represent a long-term solution for a bearing arrangement or a turbocharger. 
         [0009]    A first object of the present invention is to provide a bearing arrangement which is improved over the related art, and which allows the secure bearing of a shaft in a turbocharger with simple assembly and low costs. 
         [0010]    A second object of the present invention is to provide a turbocharger having such a bearing arrangement. 
         [0011]    The present invention provides a bearing arrangement for a turbocharger, including a bearing housing which extends in an axial direction, an anti-friction bearing, situated within the bearing housing, having an outer bearing ring and a number of rolling bodies, and an axially extending shaft which is rotatably mounted within the bearing housing. It is provided that the shaft includes a rolling body raceway for guiding the rolling bodies. 
         [0012]    The present invention takes into account the fact that there is concern for increased assembly effort as well as impairment of the bearing components, and thus of the function of the turbocharger, as the result of using a plurality of separate bearing components. This is particularly true with regard to the inner bearing rings that are usually used, which have corresponding raceways at their outer periphery for guiding rolling bodies. During assembly, the inner bearing rings are pushed onto the shaft, and must be pressed onto the shaft so that no twisting relative to the shaft is possible during operation. During the pressing, the bearing rings are compressed in such a way that the axial distance between the rolling body raceways is reduced, and thus the shaft play is changed. In addition, the diameters of the rolling body raceways, and thus also the bearing play, change. 
         [0013]    In addition, pressing the inner bearing rings may result in misalignment of same on the shaft. For example, it is possible that the inner bearing rings are not coaxially aligned with the shaft and with one another, which may result in undesirable seating at the axial contact points between the bearing rings or the bearing seats during balancing as well as during subsequent operation. Furthermore, the balance quality may deteriorate over the running time of the bearing, resulting in increased wear of the bearing components. In any case, it is thus not possible to ensure problem-free functioning of a turbocharger. 
         [0014]    Lastly, the present invention recognizes that the above-mentioned problems may surprisingly be overcome when the shaft includes a rolling body raceway for guiding the rolling body. The use of inner bearing rings to be separately installed may be dispensed with entirely. In other words, the shaft itself takes over the function of the inner bearing rings, so that a secure bearing of the shaft in a turbocharger may be achieved by this type of configuration at low cost and with ease of assembly. 
         [0015]    In addition, the sum of the component tolerances may be reduced by dispensing with separate inner bearing rings. The usually additive shape and position defects of the inner bearing rings on the shaft may thus be avoided, so that the overall tolerance is smaller. 
         [0016]    The shaft may be made of various materials, heat- and corrosion-resistant materials being particularly suited. The shaft may be manufactured in one piece, for example, with the aid of a shaping process, a machining process, or a casting process. As an alternative to the one-piece manufacture, multi-part manufacture is possible. The rolling body raceway is integrated into the lateral surface of the shaft, and may, for example, be introduced directly into the lateral surface in one step during manufacture of the shaft. Alternatively, the rolling body raceway may be subsequently introduced into the lateral surface in a step following the manufacture of the shaft base body. To ensure the necessary stability of the shaft, the shaft preferably undergoes a finishing operation after manufacture. 
         [0017]    The shaft is rotatably mounted within a bearing housing in the installed state. For this purpose, the bearing housing preferably has a hollow cylindrical design. Due to the high stresses during operation of a turbocharger, in particular heat- and corrosion-resistant metallic materials are suited for manufacturing the bearing housing. The bearing housing is in particular provided with a location hole for the further components of the bearing arrangement such as the anti-friction bearing. 
         [0018]    The anti-friction bearing and the individual anti-friction bearing components are also advantageously made of heat- and corrosion-resistant materials, for example through-hardened steels or also ceramics. The common types of bearings, for example cylindrical roller bearings or also tapered roller bearings, are basically usable as anti-friction bearings. Ball bearings, such as double-row angular-contact ball bearings in particular, are particularly suited. Two rolling body raceways situated at an axial distance from one another are advantageously introduced into the lateral surface of the shaft for guiding the rolling bodies of a double-row angular-contact ball bearing. 
         [0019]    The anti-friction bearing is also provided with at least one outer bearing ring, on the inner periphery of which a rolling body raceway is introduced, which likewise is used for guiding and positioning the rolling bodies. In this regard, one-piece as well as multi-piece manufacture of the outer bearing ring is possible. For multi-piece manufacture, the outer bearing rings may, for example, abut one another, thus preventing axial displacement of the bearings on the shaft. Alternatively, the outer bearing rings may be situated at an axial distance from one another with the aid of a spring element, for example. 
         [0020]    In particular a space, for example as a gap which surrounds the outer bearing ring, for a so-called quenching oil film is provided between the outer diameter of the outer bearing ring and the inner periphery of the bearing housing. In this case, the quenching oil film takes over the function of the vibration damper and prevents undesirable contact between the outer bearing ring and the bearing housing. 
         [0021]    To supply the space with oil, a number of supply holes may be introduced within the bearing housing, via which oil may be metered from the engine oil circuit into the space. For this purpose, the supply holes are in communicating connection with a number of the grooves surrounding the outer periphery of the outer bearing ring. Similarly, the grooves may be acted on by oil via the supply holes. Starting from the grooves, the oil may be distributed over the periphery of the outer bearing ring in the axial direction, so that a uniform oil film forms between the outer bearing ring and the inner wall of the bearing housing. The number of supply holes and of the grooves is unlimited in principle, and may be adapted, for example, to the dimensions of the bearing housing and the thickness of the quenching oil film. 
         [0022]    Furthermore, an outlet hole which is in communicating connection with a drainage groove which surrounds the outer bearing ring on its outer periphery is preferably additionally introduced into the bearing housing. It is thus ensured that the oil supplied to the space via the supply hole may continuously drain off 
         [0023]    Alternatively, the outer bearing rings may be guided in the bearing housing via an additional support ring. In this case, the support ring is embedded in the space. The support ring preferably has a number of circumferential grooves on its outer periphery, which in the installed state are in communicating connection with the supply holes in the bearing housing. The quenching oil film is then correspondingly provided in the space between the outer periphery of the support ring and the inner wall of the bearing housing. When a support ring is used, a drainage groove which is introduced into the support ring on its outer periphery is advantageously in communicating connection with an outlet hole, and appropriately allows oil drainage. 
         [0024]    Securing elements may be used to position the anti-friction bearing within the bearing housing with anti-twist protection. In principle, a plurality of securing elements is conceivable which withstand the forces acting during operation of a turbocharger and which allow an arrangement of the outer bearing ring within the bearing housing with anti-twist protection. The securing elements, the number of which is not limited in principle, may be designed, for example, as securing pins or securing bolts which may be inserted into holes provided for this purpose within the bearing housing. Alternatively, the securing elements may be designed as springs which may engage with depressions or grooves provided for this purpose. 
         [0025]    In one advantageous embodiment of the present invention, the shaft, at least in the area of the rolling body raceway, is made of a steel. In principle, various steels or metallic materials are usable here. An alloyed anti-friction bearing steel is particularly suited. For example, an anti-friction bearing steel of type 81MoCrV42-16 may be used, which in particular due to its heat stability and corrosion resistance meets the necessary requirements for use in turbochargers. The properties of the metallic material or of the anti-friction bearing steel may be influenced by the selection of the alloy components or by the composition. In principle, it is possible to produce the entire shaft from an anti-friction bearing steel. Alternatively, an anti-friction bearing steel may be used only at the locations of the rolling body raceways. 
         [0026]    In another advantageous embodiment of the present invention, the shaft is composed of a number of axially adjacent shaft sections. The individual shaft sections may be welded together prior to assembly of the bearing arrangement. The multi-piece configuration allows, for example, the controlled introduction of recesses into the shaft. These recesses provide an air volume within the shaft, which in the installed state of the shaft in the turbocharger reduces the thermal conduction from the turbine wheel to the anti-friction bearing. 
         [0027]    The costs for manufacturing the shaft and for manufacturing the bearing arrangement may be reduced in particular by using multiple shaft sections. This is made possible in particular in that the shaft sections may be made of various materials. The shaft sections into which the rolling body raceways are introduced are preferably made of an anti-friction bearing steel which has the required stability. Requirement-specific material, and accordingly less expensive shaft material, may be used for the further shaft sections. 
         [0028]    The shaft sections are preferably joined to one another by welding. Welding processes are particularly suited in this regard, since their use provides the option of also joining materials having different physical properties, for example joining steel to aluminum. 
         [0029]    The shaft preferably includes an inner recess. The inner recess may be designed as a cavity which provides an additional air volume. For example, the thermal conduction from the turbine wheel to the bearing may be reduced in this way. In addition, the recess may be used for accommodating a so-called welding discharge which arises during the joining of the shaft to the turbine wheel or also during the joining of multiple shaft sections to one another, and which may then become caught within the recesses. In principle, a recess may also be introduced into the turbine wheel. The same applies to a multi-piece configuration of the shaft for the individual shaft sections, which likewise may each be provided with a recess. This further increases the interior air volume and further reduces the thermal conductivity. 
         [0030]    The shaft preferably has a shaft journal on the end-face side for centering and fastening to a turbine wheel. The shaft journal is preferably designed as a journal which extends in the axial direction, and which in the installed state may engage with the hole in a turbine wheel. Thus, a connection between the components is possible even before the components are welded, which simplifies the subsequent welding process. In principle, providing a journal on the turbine wheel is also possible, in which case the journal engages with a hole at the end face of the shaft. 
         [0031]    It is also possible in principle to introduce a recess into the journal which provides an air volume within the shaft. The thermal conduction from the turbine wheel to the anti-friction bearing may thus also be reduced with the aid of the journal. 
         [0032]    The outer bearing ring advantageously includes a splash oil hole for acting on the anti-friction bearing with lubricant. The splash oil holes are connected to the grooves in the outer ring. The oil may pass from the grooves into the bearing space via the splash oil holes, thus being utilized for lubrication and cooling. 
         [0033]    The shaft also preferably includes a number of grooves on its outer periphery for positioning sealing elements. The grooves may be introduced into the outer periphery of the shaft on the compressor side as well as on the turbine side, thus achieving a sealing effect on both sides of the shaft. The required lubrication of the anti-friction bearing positioned within the bearing housing, which is achieved via splash oil holes, for example, may be ensured in this way. 
         [0034]    The shaft also preferably includes an oil separator. The oil separator may, for example, be mounted on the shaft as a separate component, or also integrated into the shaft. In particular, the oil separator is designed as an oil separator which operates by making use of the centrifugal force principle. 
         [0035]    The second object of the present invention is achieved according to the present invention by a turbocharger, including a compressor wheel, a turbine wheel, and a bearing arrangement corresponding to the above-mentioned embodiments, the compressor wheel and the turbine wheel being situated at the opposite ends of the shaft. It is provided that the shaft is welded to the turbine wheel. 
         [0036]    As explained at the outset, the turbine wheel of the turbine of a turbocharger is set into rotation by an exhaust gas flow, and drives the compressor via the shaft. The compressor draws in and compresses air. The compressor operates continuously, and is characterized by a small pressure rise and a high volumetric flow rate. The compressed air is conducted into the engine, a large quantity of air entering into the cylinders during the induction stroke due to the increased pressure. As a result, the oxygen content required for the combustion of fuel correspondingly increases, so that more oxygen enters into the combustion chamber of the engine with each intake stroke. 
         [0037]    The shaft is welded to the turbine wheel to achieve a secure attachment of the turbine wheel to the shaft, and thus to be able to ensure a connection between the compressor wheel and the turbine wheel. Various welding processes are suited for this purpose. 
         [0038]    For example, a friction welding process may be used. Friction welding allows secure joining of components for the same or also different material combinations. This involves a pressure welding process, the heating of the parts to be joined being produced by mechanical friction. The heating is generally produced by a movement between a rotating component and a stationary component, which are joined together under force without filler metal. 
         [0039]    As an alternative to the friction welding process, the shaft may also be joined to the turbine wheel with the aid of an electron beam welding process. Due, for example, to the high energy density that is introduced into the welding zone, this process allows the joining of a variety of different materials such as high-melting metals. Electron beam welding allows high welding speeds with extremely deep, narrow weld seams. Warping may be kept very low due to the small weld seam widths and the high degree of parallelism. 
         [0040]    Laser beam welding, for example, is also conceivable, thus allowing joining of components at a high welding speed, having a thin, narrow weld seam shape, and with low thermal warping. Laser beam welding is generally carried out without supplying a filler metal. 
         [0041]    The turbine wheel is preferably pressed onto the shaft. This procedure is advantageously carried out prior to the welding process. For this purpose, the shaft is provided on the turbine side, for example with a shaft journal which extends in the axial direction and which is pressed into a hole in the turbine wheel. Due to this press fit, a connection between the shaft and the turbine wheel is possible even before the welding, so that the two components subsequently need to be welded together only at the preferably flat contact points. As an alternative, of course, the turbine wheel may be provided with a journal, and the shaft may be provided with a hole at its end face, so that the shaft is pressed into the turbine wheel. 
         [0042]    The compressor wheel is advantageously fastened to the shaft with the aid of a nut. For this purpose, the compressor wheel is pushed onto the shaft during assembly, and lastly is clamped at that location with the aid of the nut. A secure connection also between the compressor wheel and the shaft is ensured in this way. 
         [0043]    In principle, the bearing components of the bearing cartridge may be preassembled and pushed into the bearing housing starting from the turbine side. This allows delivery of the bearing cartridge with less effort and with low assembly effort for customers. 
         [0044]    Further advantageous embodiments are provided in the subclaims directed to the bearing arrangement, which may be analogously transferred to the turbocharger. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0045]    Exemplary embodiments of the present invention are explained below with reference to a drawing.  FIGS. 1 through 4  each show a turbocharger having a bearing arrangement in a longitudinal section. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]      FIG. 1  shows a turbocharger  1  having a bearing arrangement  3 . The turbocharger has a compressor wheel  5  and a turbine wheel  7  situated at the opposite ends of a shaft  9  which extends in the axial direction. 
         [0047]    Shaft  9  is part of bearing arrangement  3 , and is rotatably mounted within a bearing housing  11  which likewise extends axially. Bearing arrangement  3  also includes an anti-friction bearing  13 , having two axially adjacent outer bearing rings  15 ,  17 , situated within bearing housing  11 . Outer bearing rings  15 ,  17  are situated at a distance from one another with the aid of a pretensioned spring element  19  situated in between. 
         [0048]    Anti-friction bearing  13  also has rolling bodies  21  designed as spheres, which in each case are held in rows in cages  23 . Rolling bodies  21  are each guided in rolling body raceways  25 ,  27  which are integrated into the lateral surface of shaft  9 . Rolling body raceways  25 ,  27  are introduced into the lateral surface in one step directly during manufacture of the shaft. The use of inner bearing rings to be separately installed may thus be dispensed with, since shaft  9  takes over the function of the inner bearing rings. 
         [0049]    This reduces the effort during assembly, in which the inner bearing rings must be pushed onto the shaft and pressed onto same. In addition, the axial distance between rolling body raceways  25 ,  27  always remains the same, so that the shaft play does not change either. 
         [0050]    In addition, the sum of the component tolerances may be reduced by dispensing with separate inner bearing rings. The usually additive shape and position defects of the inner bearing rings on shaft  9  may thus be avoided, so that the overall tolerance is smaller. 
         [0051]    Entire shaft  9  is manufactured in one piece from a heat-resistant anti-friction bearing steel. The shaft is welded to turbine wheel  7  with the aid of a friction welding process, thus achieving a secure connection between shaft  9  and turbine wheel  7 . 
         [0052]    In addition, recesses  29 ,  31  are introduced into shaft  9  as well as into turbine wheel  7 . Recesses  29 ,  31  provide an air volume, so that the thermal conduction from turbine wheel  7  to anti-friction bearing  13  during operation of turbocharger  1  is reduced. Furthermore, the recesses provide space for welding discharge during machining of the shaft. 
         [0053]    Shaft  9  is connected to compressor wheel  5  on the side opposite from turbine wheel  7 . For this purpose, compressor wheel  5  is pushed onto the shaft and is clamped at that location with the aid of a nut  33 . 
         [0054]    Grooves  35  for positioning sealing elements  37  are introduced on the outer periphery of shaft  9 . Sealing elements  37  seal against leaks and contaminants, on the sides of compressor wheel  5  as well as on the sides of turbine wheel  7 . 
         [0055]    For assembling the turbocharger, the bearing components may be preassembled and pushed into bearing housing  11  starting from the turbine side. Since the outer diameter of outer bearing rings  15 ,  17  is slightly smaller than the inner diameter of bearing housing  11 , a gap-shaped space  39  results between bearing housing  11  and outer bearing rings  15 ,  17 . Space  39  is acted on by oil via supply hole  41  in bearing housing  11 , so that a quenching oil film forms at that location. Supply holes  41 ,  42  are in communicating connection with grooves  43 ,  44  on the outer periphery of outer bearing rings  15 ,  17 . In addition, the oil, starting from grooves  43 ,  44 , is distributed into the bearings through splash oil holes  45 ,  46  connected to grooves  43 , and may thus be used for lubrication. An outlet hole  47  is included for drainage. 
         [0056]    In addition, an oil separator  49  which operates according to the centrifugal force principle is mounted on shaft  9 . 
         [0057]      FIG. 2  shows another turbocharger  61  having a bearing arrangement  63 . Turbocharger  61  has a compressor wheel  65  and a turbine wheel  67  which are situated at the opposite ends of a shaft  69  which extends in the axial direction. In  FIG. 2  as well, the entire shaft  69  is manufactured in one piece from a heat-resistant steel. 
         [0058]    Since the function and the individual components of turbocharger  61  in  FIG. 2  essentially correspond to those of turbocharger  1  in  FIG. 1 , at this point reference is made to the detailed description and illustration in  FIG. 1 , which may be analogously transferred to the discussion below. 
         [0059]    In contrast to  FIG. 1 , turbine wheel  67  is connected to shaft  69  with the aid of electron beam welding. For this purpose, turbine wheel  67  is pressed onto shaft  69 . Turbine wheel  67  has a corresponding hole  111  into which shaft journal  113  of the shaft is pressed at the end face of the shaft. Shaft journal  113  is designed as a journal which extends in the axial direction. 
         [0060]    Turbine wheel  67  and shaft  69  are subsequently welded only at flat contact surfaces  115  of turbine wheel  67  and of shaft  69  by an electric beam. 
         [0061]    Furthermore, shaft  69  is clamped to compressor wheel  65  on the side opposite from turbine wheel  67  with the aid of a nut  93 . In addition, an oil separator  109  which operates according to the centrifugal force principle is mounted on shaft  69  on the same side. 
         [0062]      FIG. 3  shows another turbocharger  121  having a bearing arrangement  123 . Turbocharger  121  likewise has a compressor wheel  125  and a turbine wheel  127  which are situated at the opposite ends of a shaft  129  which extends in the axial direction. Shaft  129  is rotatably mounted within a bearing housing  131  which likewise extends axially. 
         [0063]    For this purpose, bearing arrangement  123  has an anti-friction bearing  133 , having two axially adjacent outer bearing rings  135 ,  137 , within bearing housing  131 . Outer bearing rings  135 ,  137  are situated at a distance from one another with the aid of a pretensioned spring element  139  situated in between. Anti-friction bearing  133  also has rolling bodies  141  designed as spheres, which in each case are held in rows in cages  143 . Rolling bodies  141  are each guided in rolling body raceways  145 ,  147  which are integrated into the lateral surface of shaft  119   129 . 
         [0064]    In the installed state, a gap-shaped space  159  which is acted on by oil via two supply holes  161  in bearing housing  131  is provided between the outer diameter of outer bearing rings  135 ,  137  and bearing housing  131 . A quenching oil film forms in the space. Supply holes  161 ,  162  are in communicating connection with grooves  163 ,  164  on the outer periphery of outer bearing rings  135 ,  137 . Starting from grooves  163 ,  164 , the oil is additionally distributed into the bearings via splash oil holes  165 ,  166 , and may thus be used for lubrication. An outlet hole  167  is also included for drainage. 
         [0065]    The difference in turbocharger  121  from turbochargers  1 ,  61  previously shown lies in the nature of shaft  129 . Shaft  129  is composed of various shaft sections  171 ,  173 ,  175 . Accordingly, rolling body raceways  145 ,  147  are introduced into only one shaft section  173 . Shaft section  173  correspondingly takes over the function of the inner bearing rings which would otherwise be necessary. 
         [0066]    Shaft section  173  is composed of heat-resistant steel, whereas the two axially adjacent shaft sections  171 ,  175  are made of a less expensive, requirement-specific metallic material. 
         [0067]    Shaft sections  171 ,  173 ,  175  have axially inwardly extending recesses  176 ,  177 ,  178 ,  179 . Inner recesses  176 ,  177 ,  178 ,  179  are designed as cavities which provide an additional air volume. For this reason, they cause a reduction in the thermal conduction from turbine wheel  127  to the bearings. Turbine wheel  127  also has a recess  180  which additionally increases the air volume and thus reduces the thermal conduction. 
         [0068]    In the present case, shaft sections  171 ,  173 ,  175  are welded together. After shaft sections  171 ,  173 ,  175  are welded, shaft section  175  is lastly welded to turbine wheel  127 . For this purpose, friction welding is used, as previously described for turbocharger  1  according to  FIG. 1 . 
         [0069]    Lastly, welded shaft sections  171 ,  173 ,  175 , i.e., shaft  129 , is/are welded to turbine wheel  127  at the side of shaft section  175  with the aid of a friction welding process. Turbine wheel  127  also has an inner recess  180 , which further decreases the air volume for reducing the thermal conduction from turbine wheel  127  to anti-friction bearing  133  during operation of turbocharger  121 . 
         [0070]    Compressor wheel  125  is fastened to shaft  129  by pushing the compressor wheel onto shaft  129  on the side of the shaft opposite from turbine wheel  127 , and is fastened at that location with the aid of a nut  153 . In addition, an oil separator  169  which operates according to the centrifugal force principle is mounted on shaft  129 . 
         [0071]      FIG. 4  shows another turbocharger  181  having a bearing arrangement  183 . Turbocharger  181  has a compressor wheel  185  and a turbine wheel  187  situated at the opposite ends of a shaft  189  which extends in the axial direction. Shaft  189  is rotatably mounted within a bearing housing  191  which likewise extends axially. 
         [0072]    Bearing arrangement  183  also includes an anti-friction bearing  193 , having two axially adjacent outer bearing rings  195 ,  197 , situated within bearing housing  191 ; the outer bearing rings, the same as in the preceding figures, are situated at a distance from one another with the aid of a pretensioned spring element  199  situated in between. Anti-friction bearing  193  also has rolling bodies  201  designed as spheres, which in each case are held in rows in cages  203 . Rolling bodies  201  are guided in rolling body raceways  205 ,  207 . 
         [0073]    Since the function and the individual components of turbocharger  181  in  FIG. 4  essentially correspond to those in the exemplary embodiments previously described, at this point reference is made to the detailed description there, which may be analogously transferred to the discussion below. 
         [0074]    The same as in  FIG. 3 , shaft  189  is manufactured from three separate shaft sections  237 ,  239 ,  241 . Shaft sections  237 ,  239 ,  241  are made of various materials, shaft section  239  being made of heat-resistant steel. The two other shaft sections  237 ,  241  are made of a less expensive metallic material. 
         [0075]    Rolling body raceways  205 ,  207  are accordingly introduced only into shaft section  239 , which is made of the steel. Shaft section  239  takes over the function of the inner bearing rings, so that the costs as well as the assembly effort are reduced, and the accuracy is increased. 
         [0076]    Shaft section  239  is provided on each end face with two axially extending shaft journals  243 ,  245 . In the installed state, these shaft journals  243 ,  245  engage with holes  247 ,  249  which in each case are provided at the axial contact points of shaft sections  237 ,  241 . Shaft journals  243 ,  245  are appropriately pressed into holes  247 ,  249  during assembly. Thus, a connection between the components is possible even before the components are welded, which simplifies the subsequent welding process. The individual shaft sections are welded together only at contact surfaces  251 ,  253  due to the press fit between same. 
         [0077]    For fastening to turbine wheel  187 , shaft section  241  additionally has a shaft journal  255  on the side opposite from hole  249  which is pressed into hole  257  in turbine wheel  187 . After the pressing, the two components, i.e., shaft  189  and turbine wheel  187 , are welded to contact points  259 . Laser beam welding is used for this purpose, thus allowing joining of components at a high welding speed, having a thin, narrow weld seam shape, and with low thermal warping. Laser beam welding is carried out without supplying a filler metal. 
         [0078]    For fastening compressor wheel  185  to shaft  189 , the compressor wheel is pushed onto shaft  189  on the side opposite from turbine wheel  187 , and is clamped at that location with the aid of a nut  213 . A secure connection also between compressor wheel  185  and shaft  189  is ensured in this way. In addition, an oil separator  229  which operates according to the centrifugal force principle is mounted on shaft  189 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  turbocharger 
           3  bearing arrangement 
           5  compressor wheel 
           7  turbine wheel 
           9  shaft 
           11  bearing housing 
           13  anti-friction bearing 
           15  outer bearing ring 
           17  outer bearing ring 
           19  spring element 
           21  rolling body 
           23  cage 
           25  rolling body raceway 
           27  rolling body raceway 
           29  recess 
           31  recess 
           33  nut 
           35  groove 
           37  sealing element 
           39  space 
           41  supply hole 
           42  supply hole 
           43  groove 
           44  groove 
           45  splash oil hole 
           46  splash oil hole 
           47  outlet hole 
           49  oil separator 
           61  turbocharger 
           63  bearing arrangement 
           65  compressor wheel 
           67  turbine wheel 
           69  shaft 
           71  bearing housing 
           73  anti-friction bearing 
           75  outer bearing ring 
           77  outer bearing ring 
           79  spring element 
           81  rolling body 
           83  cage 
           85  rolling body raceway 
           87  rolling body raceway 
           89  recess 
           91  recess 
           93  nut 
           95  groove 
           97  sealing element 
           99  space 
           101  supply hole 
           102  supply hole 
           103  groove 
           104  groove 
           105  splash oil hole 
           106  splash oil hole 
           107  outlet hole 
           109  oil separator 
           111  hole 
           113  shaft journal 
           115  contact surface 
           121  turbocharger 
           123  bearing arrangement 
           125  compressor wheel 
           127  turbine wheel 
           129  shaft 
           131  bearing housing 
           133  anti-friction bearing 
           135  outer bearing ring 
           137  outer bearing ring 
           139  spring element 
           141  rolling body 
           143  cage 
           145  rolling body raceway 
           147  rolling body raceway 
           153  nut 
           155  groove 
           157  sealing element 
           159  space 
           161  supply hole 
           162  supply hole 
           163  groove 
           164  groove 
           165  splash oil hole 
           166  splash oil hole 
           167  outlet hole 
           169  oil separator 
           171  shaft section 
           173  shaft section 
           175  shaft section 
           176  recess 
           177  recess 
           178  recess 
           179  recess 
           180  recess 
           181  turbocharger 
           183  bearing arrangement 
           185  compressor wheel 
           187  turbine wheel 
           189  shaft 
           191  bearing housing 
           193  anti-friction bearing 
           195  outer bearing ring 
           197  outer bearing ring 
           199  spring element 
           201  rolling body 
           203  cage 
           205  rolling body raceway 
           207  rolling body raceway 
           213  nut 
           215  groove 
           217  sealing element 
           219  space 
           221  supply hole 
           223  groove 
           225  splash oil hole 
           227  outlet hole 
           229  oil separator 
           237  shaft section 
           239  shaft section 
           241  shaft section 
           243  shaft journal 
           245  shaft journal 
           247  hole 
           249  hole 
           251  contact surface 
           253  contact surface 
           255  shaft journal 
           257  hole 
           259  contact surface