Abstract:
An exhaust-gas turbocharger includes an outer housing, a bearing flange connected to the outer housing by a material joint, and a turbine wheel rotatable about a rotation axis. Formfittingly connected to the bearing flange is an inner housing which is formed with a collar having at least one section in contact with an inner edge of the bearing flange in a direction of the rotation axis of the turbine wheel.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. 10 2010 021 114.1-13, filed May 20, 2010, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an exhaust-gas turbocharger. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    Internal combustion engines in particular for motor vehicles are increasingly charged by fluid flow machines to further improve efficiency and thereby reduce fuel consumption. An example of a fluid flow machine is a turbocharger. The turbocharger and especially the turbocharger housing should be accurately suited to the power characteristic of the engine at hand. In order for the turbocharger to operate at high efficiency, gap dimensions have to be maintained before, during, and after operation. Temperature differences of up to several 100° C. are encountered between various operating conditions, causing the various structural parts and used materials as well as material thicknesses to undergo expansions which deviate from one another. In the event of an expansion, gap dimensions change so that the presence of an unwanted blow-by within the turbocharger may be encountered. This adversely affects efficiency. In addition, components may come into contact with one another as a result of different expansions. In the worst case scenario, components collide, causing damage or a total breakdown of the turbocharger. 
         [0005]    Another important factor in automobile construction relates to weight which should be reduced for all materials and components. Manufacturers strive therefore to optimize weight for a turbocharger, in particular of the turbocharger housing in sheet-metal construction. 
         [0006]    German Pat. No. DE 100 22 052 A1 proposes a decoupling of exhaust-conducting components and supporting and sealing outer structures. While the exhaust-conducting components of a turbocharger are exposed to high thermal stress and thus glow during operation, the thermal stress on the sealing outer structure is markedly less. However, also the outer housing is subject to very high thermal stress and flow-based stress especially in the regions of attachment onto the bearing housing of a turbocharger and also at the inflow sides of the relatively hot exhausts. 
         [0007]    The outer housing of an exhaust-gas turbocharger is normally made of unshaped sheet-metal shells which are typically welded by thermal joining with the bearing flanges. Also coupled with the bearing flanges is an inner housing of the exhaust-gas turbocharger. The inner housing normally rests against the bearing flanges or is additionally coupled with the bearing flanges by a material joint. When the inner housing rests upon the bearing flanges, different thermal expansion coefficients may cause leakage and thus may cause a blow-by. When implementing a coupling through a material joint, the heat impact zone of the thermal joining process is weakened in terms of geometry and material as a consequence of the thermal joining process. This region may thus encounter fatigue fracture and even crack formation under extreme stress conditions. 
         [0008]    It would therefore be desirable and advantageous to provide an improved exhaust-gas turbocharger to obviate prior art shortcomings. 
       SUMMARY OF THE INVENTION 
       [0009]    According to one aspect of the present invention, an exhaust-gas turbocharger includes an outer housing, a bearing flange connected to the outer housing by a material joint, a turbine wheel rotatable about a rotation axis, and an inner housing formfittingly connected to the bearing flange and formed with a collar which has at least one section in contact with an inner edge of the bearing flange in a direction of the rotation axis of the turbine wheel. 
         [0010]    The term “collar”, as used in the specification relates to a projection which represents a circular section in the inner housing. The collar points hereby with its projection in the direction of the rotation axis of the turbine wheel. A coupling of the inner housing with the bearing flange via the collar and the inner edge refers in particular to a configuration of the collar as facing away from an interior space of the inner housing so as to be able to contact the edge of the bearing flange. This is beneficial because the inner housing can be positioned in radial and axial directions in an optimum manner so that rubbing or contact of the turbine housing is prevented during operation. 
         [0011]    A formfitting coupling is ensured by a contact between inner housing and the bearing flange in at least one section via the collar and the edge. This formfitting coupling further compensates the required manufacturing tolerances as encountered during the production process of the exhaust-gas turbocharger. A turbocharger with optimized gap width can thus be realized by a coupling in accordance with the invention. 
         [0012]    According to another advantageous feature of the present invention, the collar has a bearing-flange-proximal end and is defined by a diameter which may increase in a direction toward the bearing-flange-proximal end. Thus, the diameter of the collar increases in the direction of the bearing flange to be coupled with the inner housing. As a result, the collar receives a bulged configuration. This enhances flow dynamics and the bulged or flared configuration causes an even and/or reduced stress pattern in the collar. 
         [0013]    According to another advantageous feature of the present invention, the collar and the edge may touch one another in a formfitting manner so that the collar is arranged with an undercut in relation to the edge. As the diameter of the bearing-flange-proximal end of the collar increases, the presence of a formfitting seat between the collar and the edge is established. The collar engages behind the edge so as to establish a locking function or a fit. The establishment of a particularly firm seat between inner housing and bearing flange is an important aspect of the present invention. 
         [0014]    According to another advantageous feature of the present invention, the collar has in a transition zone between the inner housing and the collar a foot region which is defined by a bending radius. Currently preferred is a configuration of the collar in the form of a collared hole. The collared hole extends from the inner housing and includes in relation to the inner housing a foot region in which the collar merges in a substantially funnel-shaped and/or cylinder-shaped collar portion. The foot region can be defined by a bending radius which does not necessarily have to be constant but may vary about the rotation movement. As a result, the foot region in particular, i.e. the transition between inner housing and collar, provides the turbocharger with a beneficial stress pattern. 
         [0015]    According to another advantageous feature of the present invention, the edge may have a geometry which is complementary to a geometry of the bending radius of the foot region. The edge and the collar thus bear upon one another at least in one area to further promote an advantageous formfitting coupling. This is beneficial in particular when positioning the inner housing in radial and axial directions and in terms of a dimensional precision of the inner housing during operation of the turbocharger. 
         [0016]    According to another advantageous feature of the present invention, the collar and the edge touch one another with flat contact at least in one area of the bending radius of the foot region. This has a positive effect on the operation of the turbocharger. Any encountered expansions of components and resultant stress are thus streamlined in such a way as to establish a firm and tight seat between inner housing and bearing flange during the entire operation in the absence of critical stress peaks. 
         [0017]    According to another advantageous feature of the present invention, the collar and the edge may touch one another with flat contact in the direction of the rotation axis of the turbine wheel at least in one contact area which is oriented in the direction of the rotation axis of the turbine wheel. This results in a length in which the collar of the inner housing flatly contacts the edge of the bearing flange. The central orientation axis of the contact area extends hereby oriented essentially in the direction of the rotation axis of the turbine wheel. This is beneficial because of the presence of elastic reserves of the inner housing and the collar. Stress caused by different thermal expansions of components can be dispersed in particular in the contact area in the direction of the rotation axis of the turbine wheel to thereby extend the life of a turbocharger according to the invention. 
         [0018]    According to another advantageous feature of the present invention, the inner housing may be made of two half-shells, with one of the half-shells facing the bearing flange and having an S-shaped configuration. The collar may be a component of an end portion of the S-shaped configuration. This reduces costs for manufacturing the half-shell. As a result of the S-shaped configuration, the half-shell can be manufactured in one operating step in a forming tool. Moreover, again any stress encountered in the inner housing and also between the inner housing and the outer housing can be advantageously compensated in a spring-like manner by the S-shaped configuration. As a result, the inner housing can expand in relation to the outer housing without adversely affecting the efficiency or the operation of the exhaust-gas turbocharger. 
         [0019]    According to another advantageous feature of the present invention, the inner housing can have a wall thickness of less than 1.5 mm. Currently preferred is a wall thickness of less than 1 mm. As a result of the coupling of the inner housing with the bearing flange in accordance with the present invention, the wall thickness for the inner housing can be selected very small. Thus, there is less residual stress within the inner housing and there is less heat introduction into the inner housing especially during assembly when compared to a great wall thickness. The exhaust-gas turbocharger can therefore be brought more rapidly to operating temperature and thus operates in an optimum efficiency range. Furthermore, the overall system of the internal combustion engine and also the exhaust-gas aftertreatment can be brought more rapidly to operating temperature so that the starting behavior of for example a catalytic converter produces less emission during the start-up phase. 
         [0020]    According to another advantageous feature of the present invention, the collar and the edge may be coupled with one another by a material joint. Currently preferred is a coupling of the collar and the edge by a radial circumferential weld seam. To further reinforce the coupling between inner housing and bearing flange, the formfitting connection may be supplemented by a material joint. This has a positive effect on the life of the connection as well as on the tightness of the connection. 
         [0021]    According to another advantageous feature of the present invention, the collar can engage behind the edge and can be coupled with the edge through thermal joining in a circumferential joining zone at a bearing-flange-proximal end of the collar. This prevents the weld seam from direct exposure to the flow of hot exhaust gas. A weakening in this region as a result of heat impact by the thermal joining process and the presence of the weld seam is of no consequence as this region is not directly exposed to the flow of hot and highly corrosive exhaust gas. Again, this extends the life of an exhaust-gas turbocharger according to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0022]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0023]      FIG. 1  is a sectional view of an exhaust-gas turbocharger according to the present invention; and 
           [0024]      FIG. 2  shows an enlarged detailed view of coupling in an area between bearing flange and inner housing. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0026]    Turning now to the drawing, and in particular to  FIG. 1 , there is shown a sectional view of an exhaust-gas turbocharger according to the present invention, generally designated by reference numeral  1 . The exhaust-gas turbocharger  1  includes an outer housing  2  and an inner housing  3  arranged in the outer housing  2 . Both the outer housing  2  and the inner housing  3  are each made of two half-shells, with the outer housing  2  comprised of a left half-shell  4  and a right half-shell  5  as relating to the drawing plane, and the inner housing  3  comprised of a left half-shell  6  and a right half-shell  7 . 
         [0027]    The half-shells  4 ,  5 ,  6 ,  7  have each a substantial S-shaped configuration. At their respective coupling zones, the half-shells  6 ,  7  of the inner housing  3  and the half-shells  4 ,  5  of the outer housing  3  overlap one another, as indicated by reference numeral  8  by way of example. The overlap  8  is configured in such a way that the right half-shells  5 ,  6  overlap the left half-shells  4 ,  6 , respectively. Furthermore, the half-shells  4 ,  5 ,  6 ,  7  are coupled to one another by a material joint in the form of a circumferential weld seam  9  The inner housing  3  is arranged on the left-hand side in relation to the drawing plane within the outer housing  2  with a sliding seat  10 . 
         [0028]    Accommodated in the inner housing  3  is a turbine wheel  11  which is supported within the exhaust-gas turbocharger  1  by a turbine wheel shaft  12 , only indicated here. The turbine wheel shaft  12  is thus determinative for the rotation axis  13  of the turbine wheel  11 . The outer housing  2  is coupled on the right-hand side as relating to the drawing plane with a bearing flange  14 . The coupling is realized by a formfit in a contact zone  15  and by a material joint in the form of a circumferential weld seam  9 . The bearing flange  14  is further provided with an inner edge  16 . The edge  16  defines an opening O within the bearing flange  14 . The opening O is traversed by a collar  17  of the inner housing  3  so that the collar  17  is able to contact upon the edge  16 . The collar  17  is defined by an internal diameter DI and an outer diameter DA which increases in the direction of the bearing flange  14 . The collar  17  thus engages behind or is arranged in undercutting relationship to the bearing flange  14  in the area of the edge  16  to establish a firm formfitting engagement. The presence of a circumferential weld seam  18  further reinforces the fixed positioning between the collar  17  and the edge  16 . 
         [0029]      FIG. 2  shows an enlarged detailed view of coupling in an area between the collar  17  of the inner housing  3  and the edge  16  of the bearing flange  14 . In the exemplary embodiment shown here, the edge  16  is illustrated with a bending radius R which extends in the direction of the bearing flange  14 . The bending radius R may be variable depending on the function and thus need not be defined as a constant. The collar  17  has a foot region  19  which corresponds to the contour of the bending radius R so as to establish a substantially flat contact. 
         [0030]    The collar  17  and the edge  16  are also in substantial flat contact in a contact area  20 , with the contact surface having a center axis  21  which is oriented substantially in the direction of the rotation axis  13  (not shown here) of the turbine wheel  11 . The inner housing  3  has a wall thickness W which is less than 1.5 mm. Currently preferred is a wall thickness of less than 1 mm. A relief clearance  22  is provided between the bearing flange  14  and the inner housing  3  to ensure a reliable seat of the inner housing  3  upon the bearing flange  14  and a good tightness in the presence of thermal expansions. 
         [0031]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.