Abstract:
A turbocharger has a turbine housing formed with a coolant inlet channel and a coolant outlet channel. The turbine housing contains a coolant separating region in which delivered coolant is separated and a coolant combining region in which coolant is combined again. Each of the coolant separating region and the coolant combining region is equipped with a conical conducting body.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an exhaust-gas turbocharger which has a cooled turbine housing. 
     Exhaust-gas turbochargers serve for improving the efficiency of an internal combustion engine and thus increasing the power thereof. For this purpose, the exhaust-gas turbocharger has a turbine with a turbine wheel and has a compressor with a compressor wheel, wherein the two rotor wheels are arranged on a common shaft. Here, the turbine wheel is driven by an exhaust-gas mass flow from a connected internal combustion engine, and in turn drives the compressor wheel. The compressor compresses inducted fresh air and conducts said fresh air to the internal combustion engine. The common shaft is mounted in a bearing housing of the turbocharger. Furthermore, the turbine wheel of the turbine is arranged in a turbine housing, and the compressor wheel of the compressor is arranged in a compressor housing. 
     An exhaust-gas turbocharger of said type must satisfy a wide variety of requirements during operation on the internal combustion engine or on an engine connected thereto. One of said requirements consists in accommodating the high temperatures which can arise in the turbocharger housing for example owing to the hot exhaust-gas mass flow. 
     Here, the conventional construction of an exhaust-gas turbocharger provides individual housings which are composed in each case of a material suited to the temperature prevailing there. Here, the compressor housing is normally composed of aluminum, whereas the bearing housing is composed of cast iron, wherein the bearing housing may additionally also be designed to be water-cooled. The turbine housing is generally composed, owing to the high temperatures that prevail in said region, of high-temperature-resistant nickel alloys. Owing to the different, suited materials for the individual housings, said housings are formed as separate parts which are connected to one another and which must furthermore be sealed off with respect to one another. 
     High-temperature-resistant nickel alloys represent a considerable cost factor. Thus, owing to the high material costs, the turbine housing constitutes the most expensive single item in the overall costs of an exhaust-gas turbocharger. 
       FIG. 1  shows the price development for nickel and aluminum in the last five years. The use of cheaper cast materials for the turbine housing, such as for example aluminum alloys, would considerably reduce the overall costs of an exhaust-gas turbocharger. Said materials are however considerably less temperature-resistant than nickel alloys. 
     So as not to exceed the maximum admissible material loads, active cooling of the exhaust-gas turbocharger may be realized by means of the cooling circuit of the internal combustion engine. Here, however, it must be ensured that the coolant pressure losses occurring in the exhaust-gas turbocharger incorporated into the cooling circuit of the internal combustion engine are as low as possible. 
     BRIEF SUMMARY OF THE INVENTION 
     It is consequently the object of the invention to specify an exhaust-gas turbocharger in which the coolant pressure losses are reduced. 
     Said object is achieved by means of an exhaust-gas turbocharger having the features as claimed. The dependent claims specify advantageous embodiments and refinements of the invention. 
     An exhaust-gas turbocharger according to the present invention has a turbine housing which has a coolant inlet duct and/or a coolant outlet duct. In the turbine housing, there are provided a coolant splitting-up region and/or a coolant merging region in which coolant delivered through the coolant inlet duct is split up, or coolant is merged to form a common coolant outlet flow, respectively. Furthermore, in the coolant splitting-up region and/or in the coolant merging region, there is arranged in each case one cone-shaped guide body which optimizes the coolant flow. 
     An exhaust-gas turbocharger having the features specified in claim  1  has the advantage that the pressure loss of the coolant passing through the turbine housing is reduced. This in turn has the advantage that the additional costs incurred in the case of the cooling of the turbine housing being incorporated into the cooling circuit of the internal combustion engine are low. In the case of the cooling of the turbine housing being incorporated into the cooling circuit of the internal combustion engine, the cooling system of the turbine housing is connected in series with the cooling system of the internal combustion engine. If pressure losses occur in the cooling system of the turbine housing, this would also have an effect on the cooling system of the internal combustion engine. For example, it would be necessary to use a coolant pump of higher power. An alternative solution would be for the cooling system of the turbine housing to use a cooling system which is independent of the cooling system of the internal combustion engine. Both of the abovementioned alternatives are however undesirably associated with additional costs. With the use of an exhaust-gas turbocharger according to the present invention, said additional costs are eliminated. 
     A further advantage of the invention consists in that, owing to the cone-shaped guide body that is used, the flow geometry in the region of the coolant inlet and also in the region of the coolant outlet of the turbine housing is more robust with respect to manufacturing tolerances than is the case with known cooling systems. The opening angle of the guide body should basically be kept as small as possible in order to prevent flow detachment. The height of the guide body can be freely selected within the limits imposed by the thickness of the cooling jacket of the turbine housing, and may advantageously be selected such that the pressure losses of the coolant passing through the turbine housing are minimized. 
     Further advantageous characteristics of the invention will emerge from the exemplary explanation thereof below on the basis of  FIGS. 2 to 8 , in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows price development for nickel and aluminum, 
         FIG. 2  shows perspective sketches illustrating an exhaust-gas turbocharger which has a wastegate and a water-cooled turbine housing, 
         FIG. 3  shows a diagram illustrating the reduction of the pressure losses in the case of cooling of the turbine housing, and the resulting positive effects on the cooling circuit of the internal combustion engine, 
         FIG. 4  shows a sketch of an exhaust-gas turbocharger, in the turbine housing of which the coolant is split between two coolant branch ducts, one of which leads to the cooling jacket of the turbine housing and the other of which leads to a coolant branch outlet of the turbine housing, 
         FIG. 5  shows a sketch illustrating a cone-shaped guide body, 
         FIG. 6  shows a sectional illustration of a part of a turbine housing which has a coolant splitting-up region, 
         FIG. 7  shows a sketch for explaining the dimensioning of the cone-shaped guide body, and 
         FIG. 8  shows a diagram illustrating the relationship between the pressure loss occurring in the turbine housing and the height of the cone-shaped guide body. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a perspective sketch illustrating an exhaust-gas turbocharger which has a wastegate and a water-cooled turbine housing. 
     The exhaust-gas turbocharger illustrated in  FIG. 2  has a compressor housing  9 , a bearing housing  10  and a turbine housing  11 . 
     In the compressor housing  9 , a compressor wheel is arranged on a common shaft in the conventional manner. In the turbine housing  11 , a turbine wheel is arranged on the common shaft in the conventional manner. The common shaft is mounted in the bearing housing  10 , which is positioned between the compressor housing  9  and the turbine housing  11 . During operation of the exhaust-gas turbocharger, the turbine wheel is driven by means of an exhaust-gas mass flow of a connected internal combustion engine, and in turn drives the compressor wheel via the common shaft. The compressor compresses inducted fresh air and conducts said fresh air to the internal combustion engine. 
     The compressor housing  9  has a fresh-air inlet  1 , through which fresh air is inducted into the exhaust-gas turbocharger from the environment, and a fresh-air outlet  2 , through which compressed fresh air is discharged in order to be conducted onward to the internal combustion engine. Furthermore, the compressor housing  9  is provided with an overrun air recirculation valve (not shown in  FIG. 2 ). Said overrun air recirculation valve has the task, during operation of the exhaust-gas turbocharger, of opening a bypass past the compressor in the event of a negative load step, such that excess charge pressure can be blown off. 
     The bearing housing  10  has a coolant inlet  7   b  and a coolant outlet  8   a . During operation of the exhaust-gas turbocharger, coolant enters the bearing housing  10  through the coolant inlet  7   b . During operation of the exhaust-gas turbocharger, coolant is discharged from the bearing housing  10  through the coolant outlet  8   a . The coolant inlet  7   b  of the bearing housing  10  is connected to a hose  7  through which coolant is transported from the turbine housing  11  to the bearing housing  10 . The coolant outlet  8   a  of the bearing housing  10  is connected to a hose  8  through which the coolant discharged from the bearing housing  10  is transported back to the turbine housing  11 . 
     The turbine housing  11  has an exhaust-gas inlet  3 , an exhaust-gas outlet  4 , a coolant inlet  5 , a coolant outlet  6 , a wastegate  12 , a coolant branch outlet  16 , and a coolant return inlet  17 . The exhaust-gas inlet  3  is connected to an exhaust-gas outlet of the internal combustion engine with which the exhaust-gas turbocharger is associated, such that during operation, the hot exhaust gas of the internal combustion engine passes into the interior of the turbine housing  11  through the exhaust-gas inlet  3 . There, said exhaust gas is conducted by a spiral arranged upstream of the turbine wheel, and then drives the turbine wheel. The turbine wheel in turn drives, via the common shaft, the compressor wheel arranged in the compressor housing. The exhaust gas exits the turbine housing  11  again through the exhaust-gas outlet  4 , which is connected to the catalytic converter of the motor vehicle. 
     During operation of the exhaust-gas turbocharger, coolant, for example cooling water, enters through the coolant inlet  5  which is provided on the underside of the turbine housing  11 . Said coolant flows through the cooling jacket of the turbine housing and is finally discharged from the turbine housing  11  again through the coolant outlet  6  provided on the top side of the turbine housing  11 . The turbine housing  11 , which during operation of the exhaust-gas turbocharger is subjected to high temperatures owing to its positioning in the hot exhaust-gas flow, is actively cooled by said coolant. As a result of the arrangement of the coolant inlet  5  on the underside of the turbine housing and the arrangement of the coolant outlet  6  on the top side of the turbine housing, automatic degassing of the coolant is advantageously attained. Gas bubbles which could hinder the coolant flow are prevented from becoming stuck within the turbine housing. 
     For the regulation of the power of the turbine wheel, a wastegate  12  is integrated into the turbine housing  11 . Said wastegate has a wastegate flap which, depending on the present demand, can be opened to a greater or lesser extent in order to conduct a desired fraction of the hot exhaust gas directly to the exhaust-gas outlet  4 , bypassing the turbine wheel. The adjustment of the opening position of the wastegate flap is realized by means of a regulator  14  which is fastened to the outside of the turbine housing  11  and which is connected via a coupling rod to a pressure capsule  13 . 
     Furthermore, the turbine housing  11  shown in  FIG. 2  has a coolant branch outlet  16  which is connected to the hose  7 . Coolant which is branched off within the turbine housing  11  is provided at said coolant branch outlet  16  and is transported through the hose  7  into the bearing housing via the coolant inlet  7   b  of the bearing housing  10 . Furthermore, the turbine housing  11  shown in  FIG. 2  has a coolant return inlet  17  which is connected to the hose  8 . The coolant discharged from the bearing housing  10  is returned into the turbine housing  11  through said coolant return inlet  17 . 
     The cooling system of the turbine housing is incorporated into the cooling circuit of the internal combustion engine, in the sense that the cooling circuit of the internal combustion engine and the cooling circuit of the turbine housing or of the exhaust-gas turbocharger are connected in series with one another. In this way, an adequately high coolant mass flow is ensured over the entire operating range of the internal combustion engine, if the coolant pressure losses occurring in the cooling system of the turbine housing or of the exhaust-gas turbocharger are low. According to the present invention, an exhaust-gas turbocharger is provided with which it is ensured that the coolant pressure losses occurring in the cooling system of the turbine housing or of the exhaust-gas turbocharger are low. In the case of the invention, this is achieved in that the pressure loss between the coolant inlet and the coolant outlet of the turbine housing is minimized by means of special guidance of the flow of the coolant in the vicinity of the external coolant ports of the turbine housing. This has a positive effect on the entire cooling circuit of the internal combustion engine. 
       FIG. 3  illustrates this effect. Here, in the diagram shown in  FIG. 3 , the volume flow rate VS of the coolant is plotted along the abscissa and the pressure P is plotted along the ordinate. If the power consumption of the coolant pump remains constant and the pressure loss of the turbine housing cooling decreases, then the coolant mass flow rate simultaneously increases. The point of intersection of the characteristic curves for the coolant pump KMP and of the cooled turbine housing TG shifts from 0) to 2). By contrast, if the coolant mass flow rate of the engine is kept constant in the case of reduced cooling losses in the turbine housing, then the power consumption of the coolant pump simultaneously falls. The point of intersection of the characteristic curves for the coolant pump and for the cooled turbine housing shifts from 0) to 1). Overall, a transition from an exhaust-gas turbocharger without turbine housing cooling to an exhaust-gas turbocharger with optimized turbine housing cooling requires only minor modifications to the cooling system of the engine. In the ideal case, it is even possible to continue to use an already existing coolant pump of the internal combustion engine, such that the incorporation of the cooling circuit of the exhaust-gas turbocharger into the cooling circuit of the internal combustion engine incurs, at most, small additional costs. 
     In an exhaust-gas turbocharger according to the present invention, the turbine housing has a coolant splitting-up region in the vicinity of its coolant inlet and has a coolant merging region in the vicinity of its coolant outlet. Splitting of the coolant to the cooling jacket of the turbine housing takes place in the coolant splitting-up region. In a further embodiment, splitting of the coolant takes place here in the sense that one of the coolant branch ducts of the cooling jacket of the turbine housing is supplied with coolant, and the other coolant branch duct delivers coolant via a coolant branch outlet of the turbine housing to the compressor housing, as is shown in principle in  FIG. 2 . 
     Both in the coolant splitting-up region and also in the coolant merging region, there is provided in each case one cone-shaped guide body which optimizes the flow guidance, as will be explained below on the basis of  FIGS. 5 to 8 . 
       FIG. 4  shows a sketch of an exhaust-gas turbocharger, in the turbine housing of which splitting of the coolant takes place to two coolant branch ducts, one of which leads to the cooling jacket of the turbine housing and the other of which leads to a coolant branch outlet of the turbine housing. 
     The illustrated exhaust-gas turbocharger has a turbine housing  11  and a bearing housing  10  connected to the turbine housing. The turbine housing  11  has a coolant inlet  5  through which cooling water is supplied to the turbine housing during the operation of the exhaust-gas turbocharger. Said cooling water is provided for example from the cooling system of the internal combustion engine. 
     Furthermore, the turbine housing  11  has a coolant outlet  6 , through which cooling water is discharged during operation of the exhaust-gas turbocharger. Said cooling water which is discharged from the turbine housing is returned to the cooling system of the internal combustion engine. 
     Furthermore, in the interior of the turbine housing  11 , there is provided a cooling jacket  23 , within which, during operation of the exhaust-gas turbocharger, coolant is transported in order to provide adequate cooling of constituent parts of the turbine housing, in particular of the wastegate flap seat and of the turbine spiral. 
     The coolant inlet  5  is connected to a coolant inlet duct  5   a . The coolant outlet  6  is connected to a coolant outlet duct  6   a.    
     In a coolant splitting-up region  5   b , a first coolant branch duct  5   d  and a second coolant branch duct  5   e  branch off from the coolant inlet duct  5   a  provided between the coolant inlet  5  and the cooling jacket  23 . The coolant branch duct  5   d  is connected to the cooling jacket  23  of the turbine housing, and the coolant branch duct  5   e  extends to a coolant branch outlet  16  of the turbine housing. A connecting hose  7  is provided between the coolant branch outlet  16  of the turbine housing and a coolant inlet  7   b  of the bearing housing  10 . 
     From the coolant inlet  7   b  of the bearing housing  10 , the coolant is conducted via a coolant inlet duct  18  of the bearing housing to a cooling jacket  22  of the bearing housing. The coolant exiting the cooling jacket  22  is conducted via a coolant outlet duct  19  of the bearing housing to the coolant outlet  8   a  of the bearing housing. From there, the coolant is returned via a connecting hose  8  to a coolant return inlet  17  of the turbine housing. The coolant return inlet  17  of the turbine housing is connected via a coolant return duct  6   e  of the turbine housing to the coolant merging region  6   b  of the turbine housing. The cooling jacket  23  of the turbine housing is connected via a coolant return duct  6   d  likewise to the coolant merging region  6   b  of the turbine housing. In the coolant merging region  6   b , the coolant returned via the coolant return ducts  6   d  and  6   e  is merged and then supplied via the coolant outlet duct  6   a  of the turbine housing to the coolant outlet  6  of the turbine housing, and said coolant is returned from there into the cooling circuit of the internal combustion engine. 
     Both in the coolant splitting-up region  5   b  and also in the coolant merging region  6   b  there is provided in each case one cone-shaped guide body  15 , as will be explained below on the basis of  FIGS. 5 to 8 . 
       FIG. 5  shows a sketch illustrating one such cone-shaped guide body  15 , as is provided, according to the present invention, in the coolant splitting-up region  5   b  of the turbine housing and also in the coolant merging region  6   b  of the turbine housing. 
     The required cooling mass flow for an exhaust-gas turbocharger with a cooled turbine housing is relatively high. Tests carried out with regard to the coolant flow in the cooled turbine housing of an exhaust-gas turbocharger with external coolant port have shown that two regions have a particularly great influence with regard to the occurring pressure losses. These are the region around the coolant inlet and also the region around the coolant outlet. The reason for this is that said regions constitute constrictions with increased flow speed, through which the entire coolant mass flow for the turbine housing must be conducted. Downstream of the inlet and upstream of the outlet, the coolant flow is split up to a greater degree and is at a lower flow speed. Since the pressure loss increases with the square of the flow speed, the cooling jacket generates a significantly lower pressure loss in relation to the coolant inlet and the coolant outlet. Consequently, the flow guidance in the coolant inlet and also in the coolant outlet has been optimized. To attain an overall improvement in the flow guidance in said regions, use is made, according to the invention, of cone-shaped guide bodies. Said guide bodies render the flow geometry more robust with respect to manufacturing tolerances, and reduce the pressure losses. The opening angle of the guide bodies should basically be kept as small as possible in order to prevent flow detachment. Said opening angle is however substantially fixedly defined by the geometric conditions of the installation space. The height of the guide bodies may be freely selected within the limits imposed by the thickness of the cooling jacket. A variation of the height of the cone-shaped guide body, as shown in  FIG. 5 , leads to an optimum value for the cone height with minimal pressure losses for the turbine housing as a whole. 
       FIG. 6  shows a sectional illustration of a part of a turbine housing according to a further exemplary embodiment, in which the turbine housing has a coolant splitting-up region. In said exemplary embodiment, the coolant supplied to the turbine housing via the coolant inlet  5  thereof is supplied through the coolant inlet duct  5   a  of the turbine housing to a coolant splitting-up region  5   b , and is split from there to the cooling jacket  23  of the turbine housing. A cone-shaped guide body  15  is provided in the coolant splitting-up region  5   b . Furthermore, in said exemplary embodiment, a coolant branch duct  5   e  is provided via which, for example, coolant for the bearing housing of the exhaust-gas turbocharger is branched off. The reference numeral  3  denotes the exhaust-gas inlet of the turbine housing. The cone-shaped guide body  15  shown in  FIG. 6  ensures that the coolant enters the cooling jacket of the turbine housing in a defined manner, and thus minimizes the pressure loss. 
       FIG. 7  shows a sketch for explaining the dimensioning of the cone-shaped guide body  15 . Here, the letter D denotes the inlet cross section of the coolant inlet duct  5   a  or the outlet cross section of the coolant outlet duct  6   a , the character a denotes the opening angle of the coolant inlet duct, the designation H 1  denotes the height of the cone-shaped guide body  15 , and the designation H 2  denotes the flow cross section at the cone flanks. 
       FIG. 8  shows a diagram illustrating the relationship between the pressure loss occurring in the turbine housing and the height of the guide body  15 . Here, the dimensionless cone height h is plotted along the abscissa, and the likewise dimensionless total pressure loss PV is plotted along the ordinate. Said total pressure loss is in relation to the kinetic pressure in the flow cross section D directly over the guide body. It is evident that, in the case of a variation of the height h of the cone-shaped guide body  15 , different values are attained for the pressure loss, and that optimum ranges exist in which the pressure loss is minimized. The following have been determined as optimum ranges:
 
0.47 ≦H   2   /D≦ 0.54
 
and
 
0.28≦ H   1   /D≦ 0.41,
 
wherein:
         H 1  is the height of the guide body  15 ;   D is the flow cross section of the coolant inlet duct  5   a  or of the coolant outlet duct  6   a , and   H 2  is the flow cross section at the cone flanks.