Abstract:
A rotor for a supercharging device may include an arrangement; the arrangement may include a compressor wheel operatively coupled to a turbine wheel. A cup-shaped bearing bush configured to receive a radial air bearing may be arranged on at least one longitudinal end of the arrangement. The bearing bush may define an interior including at least one hollow space and a plurality of stiffening ribs extending into the at least one hollow space.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent Application No. 10 2014 206 409.0, filed Apr. 3, 2014, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to the rotor of supercharging device, in particular of an exhaust gas turbocharger. The invention furthermore relates to a supercharging device with such a rotor. 
     BACKGROUND 
     From DE 10 2012 202 272 A1 a generic rotor of a supercharging device with at least two parts which are fastened to one another is known, which together enclose a hollow space. The two parts in this case are fastened to one another via subpressure that is present in the hollow space, in particular via a vacuum. The known rotor is supported via bearing bushes which are arranged alongside on the end sides. 
     From DE 10 2008 057 729 A1 an exhaust gas turbocharger for an internal combustion engine, in particular for a motor vehicle, is known, in which a rotor is supported in a stator. In order to be able to realise a particularly low-friction bearing, a pneumatic radial bearing is pneumatically charged by the rotor during the operation. 
     From DE 1 575 700 A1 a further gas-lubricated exhaust gas turbocharger is known. 
     Disadvantageous with known rotors for exhaust gas turbochargers is that these are usually formed by a solid shaft, which is comparatively heavy. If by contrast hollow bearing bushes for a radial air bearing are employed, these are light but also comparatively soft, as a result of which the natural frequency of the rotor in turn is disadvantageously impaired. 
     SUMMARY 
     The present invention therefore deals with the problem of stating an improved or at least an alternative embodiment for a rotor of the generic type, which is characterized in particular by an improved rotor natural frequency. 
     According to the invention, this problem is solved through the subject of the independent claims. Advantageous embodiments are subject of the dependent claims. 
     The present invention is based on the general idea of reinforcing or stiffening pot-shaped bearing bushes of a rotor each of which is radially air-bearing supported alongside at the ends by means of stiffening ribs, which extend into a hollow space of the respective bearing bush. The rotor according to the invention in this case comprises a compressor wheel and a turbine wheel fastened thereon, and at least on one longitudinal end the previously mentioned pot-shaped bearing bushing for the radial air bearing, wherein this bearing bush has at least one hollow space and multiple stiffening ribs extending into said hollow space. Because of the hollow embodiment of the bearing bush it is light on the one hand, which is advantageous in particular for use in exhaust gas turbochargers in a motor vehicle. On the other hand, the stiffening ribs increase the strength of the pot-shaped bearing bush, as a result of which it has significant improvements with respect to the rotor natural frequency. With the rotor according to the invention a rotor natural frequency can be achieved which is above the rotational speed of the rotor. In order to further increase the rotor natural frequency the weight at the rotor ends can be reduced, by way of which a deformation of the bearing bush through the stiffening is prevented. 
     Practically a face wall of the bearing bush is reinforced. A face wall thus reinforced again stiffens the bearing bush and contributes towards positively influencing the rotor natural frequency. Reinforcing the face wall in this case can be brought about through a convex bulge. 
     In an advantageous further development of the solution according to the invention, the stiffening ribs are formed in one piece with the bearing bush so that the bearing bush and the stiffening ribs are produced from one piece, i.e. “one casting”. This offers in particular advantages in the production of the bearing bush since no additional assembly of the reinforcing or stiffening ribs is required. 
     Practically, multiple hollow spaces and multiple stiffening ribs are provided, which are produced through axially parallel bores. The bearing bush is thus originally produced as a solid profile, wherein the hollow spaces and the stiffening ribs delimiting the individual hollow spaces are produced by bores which are subsequently introduced. Here, the bores have to be obviously distributed symmetrically to the axis of the bearing bush so as not to create an unbalance later on during operation, i.e. upon a rotation of the rotor. A bearing bush produced in such a manner is also cost-effectively producible with a high quality. Obviously it is also conceivable that the hollow spaces can be generally produced through erosion processes, as a result of which a cost-effective production of the bearing bushes is likewise realisable. 
     In a further advantageous embodiment of the solution according to the invention, the compressor wheel and the turbine wheel of the rotor each have a central recess facing one another, wherein between the compressor wheel and the turbine wheel a sealing disc is arranged, which likewise has such a central recess. At the same time, the compressor wheel, the sealing disc and the turbine wheel are screwed together by a central screw, wherein the central recess in the sealing disc and in the compressor wheel are formed for example as passage openings, whereas the recess in the turbine wheel is formed as a screw-in opening. Because of this it is possible to insert a screw connecting the three components to one another from the back of the compressor wheel, i.e. from the bearing bush of the same through the compressor wheel and the sealing disc and screw it into the turbine wheel. This makes possible clamping the three components to one another. Such a screw connection of the rotor offers in particular the major advantage of being able to easily exchange individual components of the same, for example the sealing disc arranged in the middle because of wear. 
     Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the associated figure description with the help of the drawings. 
     It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention. 
     Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference characters relate to same or similar or functionally same components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There it shows, in each case schematically, 
         FIG. 1  a sectional representation through a rotor according to the invention with a bearing bush in the region of a turbine wheel, 
         FIG. 2  a representation as in  FIG. 1 , however with a differently configured bearing bush, 
         FIG. 3  a part sectional representation and a view of a bearing bush according to  FIG. 2 , 
         FIG. 4  a representation as in  FIG. 1 , however with bearing bush that can be screwed in, 
         FIG. 5  a bearing bush that can be screwed on in a view. 
     
    
    
     DETAILED DESCRIPTION 
     According to the  FIGS. 1, 2 and 4 , a rotor  1  according to the invention of a supercharging device  2  which is otherwise merely schematically hinted, in particular of an exhaust gas turbocharger, comprises a compressor wheel  3  and a turbine wheel  4  which is indirectly fastened thereon. Between the compressor wheel  3  and the turbine wheel  4  a sealing disc  5  with multiple annular sealing fins or labyrinths  6  is arranged. The sealing disc  5  is preferentially produced from a titanium material, which minimises the heat transfer from the turbine wheel  4  to the compressor wheel  3 . On the turbine wheel side a pot-shaped bearing bush  7  for the radial air bearing is provided, which comprises at least one hollow space  8  and multiple stiffening ribs  9  extending into this hollow space. On its face wall  10 , the bearing bush  7  can have an axial bearing surface in particular a grooved axial air bearing. 
     Through the hollow design of the bearing bush  7 , the same can be formed comparatively light, i.e. with little weight, which in particular is of special advantage for using the rotor  1  in a supercharging device  2  in a motor vehicle. Because of the additionally provided stiffening ribs  9 , the strength of the bearing bush  7 , in particular in radial direction, can be significantly increased which likewise has a positive effect on a rotor natural frequency of the rotor  1 . In the case of the rotor  1  according to the invention, the rotor natural frequency can be increased via the rotational speed of the rotor  1  so that the same during the operation of the exhaust gas turbocharger is never reached and accordingly no natural frequency problems occur. In order to further increase the rotor natural frequency, the weight at the rotor ends can be reduced, by way of which a deformation of the bearing bush  7  through the stiffening is prevented. 
     According to the  FIGS. 1 and 2 , the bearing bush  7  in this case is merely provided on the turbine side, wherein it is obviously also conceivable that such a bearing bush  7  is exclusively provided on the compressor side or on both sides. 
     Looking at a face wall  10  of the bearing bush  7 , it is evident with the bearing bush  7  shown according to  FIG. 1  that the same has a convex bulge and is thereby reinforced which likewise has a positive effect on the strength and stiffness of the bearing bush  7 . The stiffening ribs  9  shown according to  FIG. 1  are annular in design and project towards the interior into the hollow space  8  collar-like. Generally, the bearing bush  7  according to  FIG. 1  merely has a single hollow space  8 . 
     In contrast with the bearing bush  7  according to  FIG. 1 , the bearing bush  7  according to  FIG. 2  comprises multiple hollow spaces  8  and multiple stiffening ribs  9 , which are produced through axially parallel bores  11  (see in particular  FIG. 3 ). In addition to producing the hollow spaces  8  by drilling, these can obviously be produced also by erosion processes. 
     Looking once more at the  FIGS. 1 and 2  it is evident that the compressor wheel  3  and the turbine wheel  4  each have a central recess  12  facing one another, just like the sealing disc  5  located between the compressor wheel  3  and the turbine wheel  4 . All three components of the rotor  1 , i.e. the compressor wheel  3 , the turbine wheel  4  and the sealing disc  5  in this case are screwed together, i.e. fastened to one another by a central screw  13 . By unscrewing the central screw  13 , disassembly of the rotor  1 , in particular for example for replacing individual components, such as for example the sealing disc  5 , is easily possible. Tightening of the screw  13  in this case is performed from the compressor side, for the purpose of which the bearing bush  7  is removed. 
     The bearing bush  7  is connected annularly sealingly to the turbine wheel  4 , in particular for example welded, soldered, upset or glued. The sealing disc  5  has two annular steps  14  and  14 ′ located opposite, wherein the compressor wheel  3  with an annular edge  15 ′ engages in one of these, whereas the turbine wheel  4  with an annular edge  15  engages in the other annular step  14 . 
     According to  FIG. 4  an embodiment is shown in which the bearing bush  7  is screwed to the turbine wheel  4 . For this purpose, the bearing bush  7  comprises an external thread  16  and the turbine wheel  4  a complementarily associated internal thread  17  (see also  FIG. 5 ). Accordingly, to disassemble the rotor  1 , the bearing bush  7  has to be first unscrewed in order to make possible access to the screw  13 . To save weight, the bearing bush  7  shown according to the  FIGS. 4 and 5  also has hollow spaces  8 . 
     In a further embodiment, the screw  13  and the bearing bush  7  in  FIG. 4  can be formed in one piece so that the three components of the rotor  1 , i.e. the compressor wheel  3 , the turbine wheel  4  and the sealing disc  5  are screwed to one another by attaching the bearing bush  7 , i.e. fastened to one another. 
     With the rotor  1  according to the invention it is possible to realise a radial air bearing at the rotor  1  with high strength in radial direction. For this purpose, the radial bearing element, i.e. concretely the bearing bush  7  comprises multiple stiffening ribs  9 , which engage in at least one hollow space  8  of the bearing bush  7  or delimit multiple of these hollow spaces  8 . Because of the stiffening ribs  9 , a deformation tendency of the bearing bush  7  in the case of high rotor rotational speed can additionally be reduced. The stiffening ribs  9  likewise have an advantageous effect on the rotor natural frequency of the rotor  1 . 
     With the rotor  1  according to the invention, the rotor natural frequency in particular can be raised above the rotational speed of the rotor  1 , so that the same exclusively rotates in a sub-critical range. This is mainly achieved through the bearing located outside and the increased stiffness.