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Time:2018-03-14 00:12Turbochargers information Click:

GmbH Automotive Continental

The invention relates to an exhaust-gas turbocharger which has a radial-axial turbine wheel.

DE 10 2009 056 632 A1 has disclosed an exhaust-gas turbocharger which comprises a radial-axial turbine wheel of said type. In the case of said known exhaust-gas turbocharger, the turbine housing has a guide element which forms at least a part of the rear wall of an inclined or oblique volute.

FIG. 1 shows a sectional view of said known exhaust-gas turbocharger. In said sectional view, the inflow direction and the outflow direction of the exhaust gas are illustrated schematically and in highly simplified form by way of an arrow. The known exhaust-gas turbocharger 1 has a turbine housing 10 with a volute 16. Within the turbine housing 10, a radial-axial turbine wheel 12 is arranged on a shaft 30. The shaft 30 is mounted in a bearing housing 20. Furthermore, a guide element 24 is provided, which is a heat shield. The latter is designed so as to form a rear wall 26 or a sub-region 28 of the rear wall of the volute 16, wherein the part of the rear wall or the rear wall is inclined at an angle of inclination β in the direction of the bearing housing. That region of the guide element 24 which is formed as a rear wall 26 or as part of the rear wall of the volute 16 or of the turbine housing 10 forms a substantially seamless transition with the volute 16 or with the turbine housing 10, such that the flow guidance of the exhaust gas is impaired to the least possible extent. The guide element 24 may, in an end region 32, be pushed or mounted onto a shoulder 34 of the bearing housing. Furthermore, the known exhaust-gas turbocharger has a tongue element 14 which preferably extends as far as a point close to the inlet edge 18 of the turbine wheel 12, such that the spacing a between the tongue element 14 and the inlet edge 18 of the turbine wheel 12 is small. Through the use of the described guide element 24 as a flow-guiding component of the turbine housing, it is possible for the axial structural space of the turbine housing to be made compact. Owing to the small spacing from the tongue element 14 to the inlet edge 18 of the turbine wheel 12, and the preferably parallel or substantially parallel arrangement of tongue angle and wheel inlet edge, the efficiency of the exhaust-gas turbocharger is increased.

The heat shield 24 of the exhaust-gas turbocharger described above is generally composed of sheet metal. This has the disadvantage that, owing to pressure influences during the assembly process and additionally owing to thermal influences during the operation of the exhaust-gas turbocharger, the heat shield is subjected to deformation. Said deformation can adversely affect the inflow to the turbine wheel, and thus the thermodynamics thereof. Furthermore, said deformation can result in an undesired collision between the heat shield and the turbine wheel. Furthermore, the stated deformation leads to thermo mechanical disadvantages with regard to functionality and the service life of the exhaust-gas turbocharger. For manufacturing reasons, at that point of the heat shield which is situated closest to the back of the turbine wheel, a corner radius is formed which adversely affects the inflow to the turbine wheel and thus the thermodynamics of the exhaust-gas turbocharger, as the exhaust-gas flow does not detach or separate cleanly. Furthermore, in practice, there is an undesired flow through the cavity between the back of the turbine wheel and the heat shield, and this is likewise associated with losses. Furthermore, owing to the stated temperature-induced deformations of the heat shield that occur during operation, a relatively large wheel rear-side space must be provided. This, too, leads to an intense and unfavorable through flow of hot exhaust gas during operation.

It is the object of the invention to specify an exhaust-gas turbocharger which is equipped with a radial-axial turbine wheel and in the case of which the abovementioned disadvantages do not arise.

Said object is achieved by means of an exhaust-gas turbocharger having the features specified in patent claim 1. Advantageous embodiments and refinements of the invention are specified in the dependent patent claims.

An exhaust-gas turbocharger having the features specified in claim 1 comprises a shaft which has an axis of rotation, a radial-axial turbine wheel which is arranged in a turbine housing and which is connected rotationally conjointly to the shaft, and a bearing housing which is arranged adjacent to the turbine housing and which has a side wall facing toward the turbine housing. Here, a sub-region of that side wall of the bearing housing which faces toward the turbine housing forms a sub-region of the rear wall of the turbine housing. That sub-region of the bearing housing which forms a sub-region of the rear wall of the turbine housing has two sub-portions, of which the first sub-portion runs obliquely with respect to the axis of rotation of the shaft in the inflow direction of an exhaust-gas flow conducted into the turbine housing, and the second sub-portion runs in a radial direction with respect to the axis of rotation of the shaft and parallel to the rear wall of the turbine wheel. The two sub-portions are connected to one another via an exhaust-gas flow separation edge of the bearing housing.

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