Abstract:
An exhaust gas turbocharging device is disclosed. The turbocharging device comprises a turbine comprising at least one flow guide vane for a medium. The flow guide vane is pivotably mounted on a housing component of the charging device by a bearing shaft seated in a recess of the housing component, wherein the bearing shaft and the recess form at least two bearing locations with different diameters spaced from each other in an axial direction.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
       [0001]    This application is a National Stage application which claims the benefit of International Patent Application No. PCT/EP2010/066921, filed Apr. 27, 2012, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a charging device, in particular turbocharger, of a vehicle, with a turbine having at least one flow guide vane for a medium, wherein the flow guide vane is pivotably mounted on a housing component of the charging device by means of a bearing shaft seated in a recess of the housing component. 
       BACKGROUND 
       [0003]    Charging devices with the features of the preamble of Claim  1  are known from the prior art. Reference is made for example to DE 1 004 766 A1, DE 698 27 504 T2 and DE 102 62 006 B4. The charging device is for example an exhaust gas turbocharger having a variable or adjustable turbine geometry (BTG). Such a variable turbine geometry with rotatably mounted flow guide vanes is prior art in modern combustion engines for passenger cars and commercial vehicles—in particular with diesel combustion engines. By using the variable turbine geometry a clear improvement of the response behaviour of the combustion engine can be achieved. By means of the adjustable flow guide vane a flow cross section of the turbine can be changed. In the process, the flow cross section is adapted for example to the operating state of the combustion engine and/or of the charging device in order to achieve a reduction of the consumption and of the emissions. The change of the flow cross section serves for adapting the damming-up behaviour of the turbine. For this purpose, the flow guide vane is rotatably or pivotably fastened to the housing component—which can also be called bearing disc. The objective here is to mount the guide vane in such a manner that over a lifespan of the charging device, a jamming of the flow guide vane is prevented, so that easy-to-operate adjusting is ensured. Insofar, the flow guide vane is to perform a defined movement within the exhaust gas flow flowing through the turbine. This is provided in particular between limitation surfaces, which for example are formed at least partially by the housing component or the bearing disc and a cover disc located opposite the latter. The flow guide vanes are actuated via an adjusting device, wherein a force required for the adjustment is introduced from outside a housing of the charging device. The flow guide vane is mounted by means of the bearing shaft, wherein the latter engages in the recess of the housing component. It is known from the prior art to embody the diameter of the bearing shaft constant over the entire length of the bearing shaft or to provide the bearing shaft with a constriction, so that it is not in contact with an inner wall of the recess at this location. The ease of operation of the bearing shaft can be improved in this manner. Such a design however renders the production of the flow guide vane or of the bearing shaft in a casting method, in particular die casting method, difficult. 
       SUMMARY 
       [0004]    Compared with this, the charging device with the features mentioned in Claim  1  has the advantage that a similar and more cost effective production is possible and in particular die casting methods can be employed without slide tools being necessary for demoulding the bearing shaft. According to the invention, this is achieved in that the bearing shaft and the recess form at least two bearing locations with different diameters that are spaced from each other in axial direction. Both the recess of the housing part as well as the bearing shaft preferentially have a round cross section. Jointly they form the at least two bearing locations. Here it is provided that the bearing location and the inner wall of the recess are in tactile contact with each other in the region of the bearing location at the most. In this manner the ease of operation of the flow guide vane or of the bearing shaft is improved, since the bearing shaft is not in tactile contact with the inner wall of the recess over its entire longitudinal extension, but only in certain parts or sections, by means of which a torque (rotational resistance) counteracting an adjusting torque is reduced. In the region of the bearing location, the diameter of the bearing shaft is called shaft diameter and the diameter of the recess, recess diameter. It is now immaterial if shaft diameter and/or recess diameter of the bearing locations differ from each other. It can be provided, both, that the shaft diameter remains constant over the entire length of the bearing shaft while the recess diameter changes in order to achieve the different diameters of the bearing locations, and also that the shaft diameter changes, while the recess diameter remains constant. It can likewise be provided that both the shaft diameter as well as the recess diameter change. It is also provided that the bearing shaft at the bearing locations has different shaft diameters and/or the recess at the bearing locations has different recess diameters. In particular, when the bearing shaft has different shaft diameters at the bearing locations, the flow guide vane or the bearing shaft can be produced with moulding production processes, without a reworking such as for example grinding being necessary. Here, a MIM or a similar process is preferred. Advantageously, the bearing locations with the different diameters are formed at least through a change of the shaft diameter. In this manner, a slide tool can be omitted, which is otherwise necessary for demoulding the bearing shaft from a casting mould used for the production. Consequently, the production of a die casting mould can be carried out simpler and/or more cost effectively because of the better de-mouldability of the bearing shaft. Instead of the MIM method, a precision casting method or the like can also be used. Owing to the low tolerances of the flow guide vane or bearing shaft so produced, finishing or reworking operations of the bearing shaft are avoided. 
         [0005]    A further development of the invention provides that the bearing location having the larger diameter is arranged on the side facing the flow guide vane. Starting out from the flow guide vane, the diameter of the bearing location therefore diminishes. In particular when the different diameters of the bearing locations are formed through different shaft diameters, the demoulding of the flow guide vane or of the bearing shaft can be facilitated in this manner. 
         [0006]    A further development of the invention provides that between the bearing locations a continuous change of the shaft diameter and/or of the recess diameter is provided. Preferentially, a sudden change of the shaft diameter or of the recess diameter is avoided, in order to keep the notch effect as small as possible. Owing to a sudden diameter change, a local stress concentration could occur at the location concerned, by means of which the load on the material at this location would be significantly increased. For this reason, the continuous diameter change is preferably provided. 
         [0007]    A further development of the invention provides that in the region of at least one of the bearing locations the recess diameter substantially corresponds to the shaft diameter. This means that the bearing shaft in this region is directly mounted on the housing component, i.e. is in tactile contact with the latter. It is thus not necessary to provide an additional intermediate element between bearing shaft and the inner wall of the recess in order to form the bearing location. Advantageously, the shaft diameter is slightly smaller than the recess diameter in order to make possible an easily operated adjustment of the flow guide vanes by means of the bearing shaft. 
         [0008]    A further development of the invention provides that the recess is present as stepped recess and/or as recess with constant diameter. In the case of the stepped recess, the recess can be achieved for example by means of bores having at least two different diameters. Thus a stepped bore is present. However, it can likewise be that the recess has a constant diameter, while the different diameters of the bearing locations are realised with different shaft diameters. 
         [0009]    A further development of the invention provides that the bearing shaft is assigned at least one bearing element. The bearing element is arranged in the region of the bearing location or assigned to the latter, so that the bearing element can at least co-form the bearing location. For example, the bearing element can be present as ring element, which is fastened on the bearing shaft or in the recess. With such a ring element it is achieved that the recess diameter can be kept constant over the length of the recess, while the different diameters of the bearing locations are realised with different shaft diameters. 
         [0010]    A further development of the invention provides that the bearing element is non-positively, positively and/or materially connected to the bearing shaft. Alternatively, the bearing element can be likewise introduced into the recess of the housing where it is non-positively, positively and/or materially fastened. 
         [0011]    A further development of the invention provides that the bearing element is part of an adjusting device for the bearing shaft, so that the adjusting device at least in certain regions interacts with the bearing shaft and the recess in order to form the bearing location. For example, the bearing element is part of an adjusting lever of the adjusting device. This adjusting lever is used in order to apply a torque onto the bearing shaft and thus adjust the flow guide vane. Here it is now provided that the bearing element engages about the bearing shaft at least in certain regions and simultaneously engages in the recess. In this manner, the recess diameter in turn can remain constant and different shaft diameters can be present in order to form the different diameters of the bearing locations. 
         [0012]    A further development of the invention provides that the bearing shaft and the guide vane are produced as a common component, in particular by means of a die casting method. Such a procedure is particularly preferred when the bearing shaft, starting out from the flow guide vane, has a decreasing shaft diameter. In this case, a slide mould for demoulding can be omitted during the production of the component so that both the production of the common component as well as a provision of the die casting mould for producing the component is easier and more cost-effectively to accomplish. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    In the following, the invention is explained in more detail by means of the exemplary embodiments shown in the drawing without any restriction of the invention taking place. It shows: 
           [0014]      FIG. 1  a charging device in cross section, 
           [0015]      FIG. 2  a flow guide vane known from the prior art with a bearing shaft in a first embodiment, 
           [0016]      FIG. 3  the flow guide vane with a bearing shaft in a second embodiment known from the prior art, 
           [0017]      FIG. 4  the flow guide vane with a bearing shaft in a first embodiment according to the invention, and 
           [0018]      FIG. 5  the flow guide vane with a bearing shaft in a second embodiment according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows a charging device  1  with a turbine  2 , in particular exhaust gas turbine, which comprises a turbine wheel  3 . The turbine wheel  3  is subject to a radial onflow via an adjustable vane system  4 , an outflow from the turbine wheel  3  takes place axially (in  FIG. 1  to the right). The adjustable vane system  4  comprises at least one flow guide vane  5 , which is arranged in the flow path of the exhaust gas flowing onto the turbine wheel  3 . The flow guide vane  5  is pivotably mounted by means of a bearing shaft  6 . To this end, the bearing shaft  6  is seated in a recess  7  of a housing component  8 —which is part of a housing  9  of the turbine  2 . The housing component  8  is for example a bearing disc  10  of the charging device  1 . Opposite the bearing disc  10 , a cover disc  11  is provided. Between bearing disc  10  and cover disc  11  the flow guide vane  5  is arranged. For adjusting the flow guide vane an adequate spacing between bearing disc  10  and cover disc  11  is necessary. In order to ensure this, a spacer  12  is additionally provided between bearing disc  10  and cover disc  11 . The flow guide vane  5  preferentially has a minor spacing both from the bearing disc  10  as well as from the cover disc  11 , in order to make possible in this way a reliable and easy-to-operate adjusting of the flow guide vane  5 . 
         [0020]    On the side of the bearing shaft  6  facing away from the flow guide vane  5  an adjusting device  13  is provided and connected to the bearing shaft  6  in a rotationally fixed manner. By means of the adjusting device  13 , a torque can be applied to the bearing shaft  6  and thus the flow guide vane  5  adjusted. By adjusting the flow guide vane  5  an onflow angle of the turbine wheel  3  can be adjusted corresponding to a load state of a combustion engine (not shown), which is assigned to the charging device  1 . Thus, for example with a low load of the combustion engine, the flow cross section in a flow channel  14 , in which the flow guide vane  5  is arranged, can be reduced. In this manner, the onflow speed of the turbine wheel  3  is sufficiently high despite the low exhaust gas mass flow through the charging device  1  or the turbine  2  in order to drive the turbine wheel  3 . Accordingly, the flow cross section of the flow channel  14  is increased with high loading of the combustion engine, which is synonymous with a large exhaust gas mass flow, so that the turbine  2  does not generate an unnecessarily high flow resistance or pressure loss and the energy contained in the exhaust gas is advantageously available for driving the turbine wheel  3 . The turbine wheel  3  driven by the exhaust gas in turn drives for example a compressor wheel (not shown) of the charging device  1  via a shaft  15 . 
         [0021]      FIG. 2  shows a first embodiment of the flow guide vane  5  know from the prior art with the bearing shaft  6 . As already described above, the latter is rotatably mounted in the recess  7  of the housing component  8  or the bearing disc  10 . With this embodiment, the recess  7  has a constant recess diameter d 1  and the bearing shaft  6  a constant bearing shaft diameter d 2 . Here it is provided that the bearing shaft diameter substantially corresponds to the recess diameter or is slightly smaller, so that an easy-to-operate adjusting of the flow guide vane  5  by means of the bearing shaft  6  is ensured. 
         [0022]      FIG. 3  shows a second embodiment of the flow guide vane  5  and the bearing shaft  6  known from the prior art. In this case, too, the bearing shaft  6  is mounted in the recess  7  of the housing component  8 . As in the exemplary embodiment shown in  FIG. 2 , the recess diameter d 1  is constant. The shaft diameter d 2  is also substantially constant. However, the bearing shaft  6  has a constriction  16  in a region, so that the diameter is reduced here (indicated in  FIG. 3  by the interrupted lines). In this way, a first bearing location  17  and a second bearing location  18  are present, at which the bearing shaft  6  is in tactile contact with the inner wall of the recess  7 . In this way, the rotational resistance of the bearing shaft, i.e. the torque, which counteracts an adjusting torque used for adjusting the flow guide vane  5  can be reduced, since the support area of the bearing shaft  6  on the inner wall of the recess  7  is reduced. 
         [0023]      FIG. 4  shows a first embodiment of the flow guide vane  5  and the bearing shaft  6  according to the invention. It becomes clear that just as in the exemplary embodiment of  FIG. 3 , two bearing locations  17  and  18  are present. In contrast with the mentioned exemplary embodiment, however, the bearing locations  17  and  18  have different diameters. Here, the diameter can for example be defined by the diameter with which the bearing shaft  6  enters into tactile contact with the inner wall of the recess  7  for forming the bearing locations  17  and  18 . Simplified, the diameter of the bearing locations  17  and  18  can be assumed with the shaft diameter in the region of the bearing locations  17  and  18 . Alternatively, the diameter can also be defined as mean value of shaft diameter and recess diameter. 
         [0024]    In the embodiment shown here, the recess  7  is a stepped recess  19  or stepped bore. This can be easily produced in that two drilling operations with different diameters are carried out. It is provided that the bearing shaft  6  in the region of the first bearing location  17 , which is located on the side of the bearing shaft  6  facing the flow guide vane  5 , has a larger diameter than in the region of the second bearing location  18 . Thus, both a stepped bearing shaft  6  as well as a stepped recess  7  are present, which jointly form the bearing locations  17  and  18 . Here it is provided that the flow guide vane  5  and the bearing shaft  6  are produced as a common component  20 . In this connection, the stepped embodiment of the bearing shaft  6  with the diameters decreasing starting out from the flow guide vane  5  is advantageous: by stepping the diameters of the bearing shaft  6  a demoulding of the flow guide vane  5  and of the bearing shaft  6  from a die casting mould is easily possible without a slide having to be provided. Above all, no damages of the bearing shaft  6  occur during the demoulding, so that reworking (for example precision turning and/or grinding) is not necessary. In the region of the first bearing location  17 , the recess has the recess diameter d 1  and the bearing shaft  6  the shaft diameter d 2 . In the region of the second bearing location  18 , the recess diameter d′ 1  and the shaft diameter d′ 2  are present. Here, d′ 1 &lt;d 1  and d′ 2 &lt;d 2  applies. 
         [0025]    By means of the bearing disc  10 , a mounting of the flow guide vane  5  is initially achieved. It is subjected to hot exhaust gas on the side facing the flow guide vane  5  and thus serves for the unilateral limitation of the flow channel  14  (turbine space). Together with the contour of the flow guide vane  5  and the cover disc  11 , it forms the nozzle geometry of the turbine  2 . Jointly with these, it is thus responsible to a high degree for the efficiency of the turbine  2 . 
         [0026]      FIG. 5  shows a second embodiment of the flow guide vane  5  and the bearing shaft  6  according to the invention. Here, these are constructed similarly in principle as in the exemplary embodiment of  FIG. 4 , so that in this connection reference is made to the latter. In contrast with the embodiment of  FIG. 4 , the recess  7  however has no stepping, i.e. is not a stepped recess  19 . The recess  7  rather has a constant diameter d 1 . In the region of the smaller shaft diameter d′ 2  a bearing element  21 , which offsets the difference between the shaft diameter d′ 2  and the recess diameter d 1 , is therefore arranged. The bearing element  21  for example is a ring element, i.e. ring-shaped. The inner diameter of the ring element in this case substantially corresponds to the shaft diameter and the outer one to the recess diameter. Here, deviations in each case of the inner and/or outer diameter can be provided in order to ensure the easy-to-operate adjusting of the flow guide vane  5 . The bearing element  21  can be fastened either on the bearing shaft  6  or in the recess  7 . In the exemplary embodiment shown here it is pressed onto the bearing shaft  6 , i.e. non-positively or frictionally connected with the latter. The bearing element  21  is part of the adjusting device  13  and thereby operationally connected to an adjusting lever  22 . For adjusting the flow guide vane  5  the adjusting lever  22  is actuated, by means of which a torque is imposed on the bearing shaft  6 , which causes the adjustment of the flow guide vane  5 . 
         [0027]    The exemplary embodiments of the flow guide vane  5  and bearing shaft  6  described by means of the  FIGS. 4 and 5  have advantages with regard to the production as already described above, since they can be easily produced as common component  20 . The different diameters of the bearing locations  17  and  18  however bring about a clear reduction of the rotational resistance during an adjusting of the flow guide vane  5 . Also advantageous are therefore embodiments, wherein the shaft diameter remains constant and the recess diameter becomes larger staring out from the flow guide vane  5 . The difference between the shaft diameter and the recess diameter in the region of the second bearing location  18  can in turn be offset by the bearing element  21  in this case.