Patent Publication Number: US-9896967-B2

Title: Turbocharger

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a turbocharger. 
     Description of the Related Art 
     A generic turbocharger is known from EP 1 256 703 B1. 
     Turbochargers of said type are used in internal combustion engines in order to increase the engine characteristic values such as power and torque and to reduce exhaust-gas emissions and specific fuel consumption. At low circumferential speeds of the compressor wheel, a temperature increase of the compressor air flow occurs at the bearing-housing-side housing wall of the compressor diffuser. Since the metal bearing housing constitutes the connecting element between the metal turbine housing and the metal compressor housing, considerable internal heat transfer takes place from the turbine side to the compressor side. In the prior art, the temperature increase arises in that, while thermally highly conductive metallic materials are used, the relatively low flow speeds generate an increased residence time of the fluid (air) in the compressor diffuser. 
     It is therefore an object of the present invention to provide a turbocharger for an internal combustion engine, which turbocharger reduces the introduction of heat from the bearing housing into the compressor diffuser in order to reduce the introduction of heat from the diffuser into the compressor air flow and to thereby increase the compressor efficiency, particularly at low circumferential speeds. 
     BRIEF SUMMARY OF THE INVENTION 
     In a particularly preferred embodiment of the turbocharger, therefore, it is provided that a radial enlargement of the bearing housing cover also covers the region of the diffuser wall of the bearing housing. To reduce the introduction of heat, the bearing housing cover is, in relation to the prior art, produced from a material with a considerably lower thermal conductivity of less than 5 W/mK and in particular of less than 1 W/mK, such as for example a temperature-resistant plastic. In this way, the thermal conductivity of the bearing housing cover can be reduced at least by a factor of 20 in comparison to metallic materials. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Further details, advantages and features of the present invention will emerge from the following description of exemplary embodiments on the basis of the appended drawings, in which: 
         FIG. 1  shows a schematically highly simplified, cut-away illustration of an exhaust-gas turbocharger; 
         FIG. 2  shows a sectional illustration of a prior art bearing housing and bearing housing cover composed of metal; and 
         FIG. 3  shows a sectional illustration of a bearing housing with a bearing housing cover composed of plastic. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematically highly simplified illustration of a turbocharger  1  which comprises a compressor  2  and a turbine  3 . The turbocharger  1  self-evidently has all the other conventional components, the description of which is however not required for the explanation of the principles according to the invention and which has accordingly been omitted. 
       FIG. 2  illustrates an enlarged sectional view of a bearing housing  4  of a prior art turbocharger  1 , which bearing housing  4  is arranged between the turbine  2  and the compressor  3  and has a metal bearing housing cover  5 . Said bearing housing cover  5  is composed of metal in the prior art as shown in  FIG. 2 , while in the present invention it is composed of a material with low thermal conductivity as shown in  FIG. 3 , for example a temperature-resistant plastic, whose thermal conductivity is less than 5 W/mK. As can be seen from  FIG. 3 , the low thermal conductivity material bearing housing cover  5 ′ has been enlarged to such an extent that it can also cover the region of the diffuser wall (not illustrated in  FIGS. 2 and 3 ) of the compressor  2 . 
     To obtain a further reduction in the heat flow from the bearing housing  4  to the bearing housing cover  5 ′, a cavity  6  is provided between the bearing housing cover  5 ′ and the bearing housing  4 . Said cavity  6  is arranged in an outer cover region  7  as viewed in the radial direction R of the bearing housing cover  5 ′. The air in said cavity  6  has a thermal conductivity which, at a maximum, is lower than that of the plastic of the bearing housing cover  5 ′ by a factor of 200, and said air thereby forms a further insulating layer between the bearing housing  4  and bearing housing cover  5 ′. 
     The bearing housing cover  5 ′ may also have a metal bush  10  in the region of a cover bore  9  which holds piston rings  8 , in order to prevent increased wear of the non-metallic bearing housing cover at the point of contact with the piston rings  8 . 
     To complement the above written disclosure, reference is made explicitly to the diagrammatic illustration in  FIGS. 1, 2 and 3  of the invention. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Turbocharger 
           2  Turbine 
           3  Compressor 
           4  Bearing housing 
           5  Bearing housing cover (metal) 
           5 ′ Bearing housing cover (low thermal conductivity material) 
           6  Cavity 
           7  Cover region 
           8  Piston rings 
           9  Cover bore 
           10  Metal bush