Abstract:
An exhaust-gas turbocharger for an internal combustion engine is described herein, in particular for a motor vehicle. An exhaust-gas side sacrificial sealing ring that serves as a heat shield is replaced by a step formed in a housing and in a hub, the step serving to assume the function of a heat shield instead of the sacrificial sealing ring. This design feature reduces production costs in connection with the outlay for the sacrificial sealing ring.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     This application claims priority to German patent application DE 10 2008 046 221.7 filed on Sep. 8, 2008, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to an exhaust-gas turbocharger for an internal combustion engine, in particular in a motor vehicle. 
     BACKGROUND 
     Document DE 10 2004 057138 A1 discloses such an exhaust-gas turbocharger of the generic type comprising an exhaust-gas side turbine wheel, an intake-side compressor wheel, and a shaft, the compressor wheel being positioned on the shaft and the turbine wheel being connected to the shaft by means of welding. A point of connection between the hub of the turbine wheel and the shaft is arranged in proximity to the bearing. Moreover, cooling ribs are described as machined on the hub, between which ribs a cooling fluid such as air, water or oil is conducted in order to eliminate heat in such a manner that less heat reaches the region of the shaft bearing. The two shaft seals mounted in the grooves of the hub prevent oil from leaking out of the bearing. The exhaust-gas side shaft seal can serve as a sacrificial sealing ring in this configuration. This design engineering is costly and also requires expensive materials. 
     SUMMARY 
     The present invention addresses the problem of providing for such an exhaust-gas turbocharger of an internal combustion engine an improved or at least a different embodiment that is characterised in particular in that reduced production and/or assembly costs result from design-engineering optimisation. 
     This problem is solved according to the invention by the subject matter of the dependent claim  1 . Advantageous embodiments are the subject matter of the dependent claims. 
     The invention is based on the general concept of replacing a sacrificial sealing ring, which is designated as such in the prior art and serves as a heat shield, with a step that is formed in the housing and in the hub, said step serving to assume the function of a heat shield instead of the sacrificial sealing ring. In dispensing with the sacrificial sealing ring, the manufacturing costs are reduced by the amount required for this sacrificial sealing ring. Since the sacrificial sealing ring furthermore is adversely affected by the effects of the from the exhaust gas and thus eventually wears down over time, which is not the case with heat shield configured as a step, the fail safety of the components in their entirety is improved by dispensing with individual components susceptible to failure. 
     Additional important features and advantages of the invention can be found in the dependent claims, in the drawings, and in the pertinent description of the figures with reference to the drawings. 
     It is understood that the features described above and those to be described in what follows can be used not only in the particular cited combination; but also in other combinations or independently without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are shown in the drawings and are described in more detail in the following description, the same reference numerals referring to components which are the same or functionally the same or similar. 
       It is schematically shown in 
         FIG. 1  an exhaust-gas side longitudinal section through an exhaust-gas turbocharger, 
         FIG. 2  an enlarged figure of the longitudinal section through an exhaust-gas turbocharger in the region of the hub with a hub step and a housing step, 
         FIG. 3  a representation as in  FIG. 2 , however with a housing step inclined toward the hub step, 
         FIG. 4  the exhaust-gas turbocharger without oil-thrower groove and with a Scania step in the region of the hub, 
         FIG. 5  the exhaust-gas turbocharger without oil-thrower groove and without a Scania step in the region of the hub, 
         FIG. 6  the exhaust-gas turbocharger with an especially configured oil-thrower groove, 
         FIG. 7  the exhaust-gas turbocharger with a labyrinth seal arranged in the region of the hub. 
     
    
    
     DETAILED DESCRIPTION 
     Corresponding to  FIG. 1 , an exhaust-gas turbocharger  1  for an internal combustion engine comprises an exhaust-gas side turbine wheel  2 , a shaft  3  that connects in a rotationally-fixed manner the turbine wheel  2  to a compressor wheel  27 , as well as a housing  4 . The shaft  3  is mounted in a bearing region  5 , the bearing comprising a bearing device  6 ,  6 ′ in a bearing-housing section  7  and a bearing-shaft section  8 , a hub  9  of the shaft  3  between bearing region  5  of the shaft  3  and turbine wheel  2 , and a hub-housing section  10  surrounding the hub  9  as well as a lubrication supply device  11  for supplying the bearing region  5  of the shaft  3  with lubrication. 
     The turbine wheel  2  is connected with the hub  9  of the shaft  3  to the shaft  3  by means of a connecting device  12 . A sealing ring  14  is positioned in a groove  13  of the hub  9  so as to prevent a flowing of the lubricant for lubricating the bearing device  6 ,  6 ′ over and beyond the sealing ring  14  in the direction of the turbine wheel  2 . If the lubricant, for example oil, comes into contact with hot exhaust gas, it can coke, and owing to the coke products, the lubrication of the shaft  3  can no longer be ensured. 
     An enlarged partial section  15  of  FIG. 1  is shown in  FIG. 2 . The enlargement makes it easier to recognise the sealing ring  14  in the groove  13  of the hub  9 . Owing to the hub-housing section  10  that closely abuts the sealing ring  14 , the bearing-region side, oil-conducting intermediate chamber  16  arranged between hub  9  and hub-housing section  10  is sealed with respect to the turbine-wheel side, exhaust-gas conducting intermediate chamber  17 . After the sealing ring  14  toward the direction of the bearing region  5 , an annular groove  18 , in particular represented here as a Scania step  19 , is formed in the hub-housing section  10 . As may be seen in  FIG. 2 , the Scania step  19  is configured with a first surface  19   a  that extends away from the hub  9 , a second surface  19   b  that intersects the first surface  19   a  and extends toward the direction of the exhaust-gas side, and a third surface  19   c  that intersects with the second surface  19   b . The third surface  19   c  intersects with the oil conducting intermediate chamber  16 . Since the sealing ring  14  comes into contact with the hot exhaust gas of the internal combustion engine on the side of the exhaust-gas conducting intermediate chamber  17 , this sealing ring  14  must be protected from too great an impact of the heat with a heat-protection shield. To this end, a radial hub step  20  is configured in the hub  9  and a radial housing step  21 , which communicates with the radial hub step  20 , is configured in the hub-housing section  10 . The radial hub step  20 , in co-operation with the radial housing step  21 , forms an effective heat-protection shield for the sealing ring  14  from the hot exhaust gas. 
     During the use of the exhaust-gas turbocharger  1 , the hot exhaust gases of the internal combustion engine arrive in the exhaust-gas conducting intermediate chamber  17  between the hub  9  and the hub-housing section  10 . There, they bounce with high speed against the housing step  21  and are thrown back against the hub step  20  positioned opposite therefrom. By means of guiding the exhaust gas in the exhaust-gas conducting intermediate chamber  17 , turbulence arise, the flow resistance is increased, and the speed with which the exhaust gas strike the sealing ring  14  is considerably reduced. The hub step  20  and the housing step  21  thus act in the style of a labyrinth seal and the sealing ring  14  is thus better protected from the direct effects of the heat of the exhaust gas. It is self-evident that the exhaust-gas conducting intermediate chamber  17 , together with the housing step  21  and the hub step  20 , is optimised with regard to the above-mentioned effect as a heat shield. 
     As  FIG. 1  shows, the shaft  3  between the bearing-shaft section  8  and the groove  13  can be configured with an oil-thrower groove  22 . This oil-thrower groove  22  has the advantage that oil that penetrates from the lubrication supply device  11  in the direction of the sealing ring  14  and that migrates from the oil-thrower groove  22  upon rotation of the shaft  3  is hurled away from the oil-thrower groove  22  in such a manner that a penetration of the oil into the oil-conducting intermediate chamber  16  is at least reduced (cf.  FIG. 2 ). 
     It can be seen from  FIG. 2  that a first intermediate chamber  23  is arranged between the hub step  20  and the housing section  21 . An axial length of the intermediate chamber  23  between the hub step  20  and the housing section  21  can be from 0.2 mm to 0.4 mm. Moreover, a second intermediate chamber  24  can be provided between the hub step  20  and hub-housing section  10 , the radial length of said second intermediate chamber between the hub step  20  and the hub-housing section  10  being between 0.2 mm and 0.4 mm. The sealing ring  14  can have an external diameter of 10 mm to 16 mm. 
     According to  FIG. 3 , it is however also possible that the plane of the of the ring surface  25  oriented toward the turbine wheel  2  is not arranged transversely to the shaft  3 , as is shown in  FIG. 2 , but rather that the ring surface  25  runs inclined in the direction of the hub step  20 . If the ring surface  25  runs inclined, it has the shape of frustoconical casing. In this manner, an angle between the ring surface  25  and a casing surface  26 , oriented in the direction of the sealing ring  14 , of the housing step  21  can be up to 180° 
     A preferred embodiment according to  FIG. 4  is equipped with an annular groove  18  in the shape of Scania step  19 ; however, there is not an oil throwing groove  22  between the groove  14  and the bearing-shaft section  8 . 
     Furthermore, an embodiment shown in  FIG. 5  is conceivable that may not have a sealing ring  14  arranged in the groove  13 , but is equipped with neither an oil throwing groove  22  nor with an annular groove  18  configured as a Scania step  19 . 
     A particular embodiment with a specially configured oil throwing groove  22 , as is shown in  FIG. 6 , has at least one annular bead  27 ,  27 ′ in the region of the oil throwing groove  22  and configured on the shaft  3 . Preferably the annular bead  27 ′ arranged in the region of the sealing ring  14  borders at least in part an annular gap  28  arranged between hub  9  and hub-housing section  10  and furthermore positioned between the sealing ring  14  and the oil throwing groove  22 . In the region of the annular gap  28 , the hub  9  can be distanced from the hub-housing section  10  by approximately 0.2 mm to 0.4 mm owing to the annular gap  28 . 
     In a further-developed embodiment, as is shown in  FIG. 7 , the hub step  20  and the housing step  21  can be configured in the shape of a labyrinth seal  29 . This can, for example, be achieved by means of concertina-like run of the gap between the hub-housing section  10  and the hub  9 , as shown.