1. Field of the Invention
The invention relates to a method and an apparatus for matching the flow capacity of a radial turbine of a turbocharger to a flow capacity of an internal combustion engine.
2. Discussion of Background
Radial turbines for turbochargers typically include at the gas inlet end, of a spiral-shaped gas inlet casing and a nozzle ring spatially terminating this casing in the direction toward the gas outlet end. The rotor, which is guided on the compressor drive shaft and is provided with vanes, is arranged at the gas outlet end. The gas flow duct extends between the rotor hub and the opposite region of the gas outlet casing. Instead of a gas outlet casing, it is also known to use a gas outlet flange which is releasably connected to the gas inlet casing by a plurality of bolts uniformly distributed on its periphery.
If a turbocharger is to be associated with a certain internal combustion engine, the swallowing capacity of the radial turbine, i.e. the size of the delivery flow processed by it for a given machine diameter, has to be correspondingly matched.
For this purpose, a method is known in which the rotor vanes and the nozzle ring vanes are first shortened by removal of material from the vane height to correspond with the parameters of the internal combustion engine. As an alternative to this and--if required--additionally also, the angle of incidence of the nozzle ring vanes can or must be modified, i.e. different nozzle rings with the required vane angle of incidence are employed. Because the gas inlet casing and the nozzle ring are accurately matched to one another, the gas inlet casing must subsequently be correspondingly matched, i.e. it must also be exchanged.
In this method, the matching of the radial turbine to correspond with the modified rotor takes place at the gas inlet end, i.e. both the nozzle ring and the spiral-shaped gas inlet casing must be exchanged. For this reason, the method is very expensive in terms of labor and is therefore costly. Because of the many combination possibilities, this requires quite a high stores holding of the corresponding exchange parts and very extensive transport requirements for the matching of the turbocharger to the corresponding internal combustion engine (which takes place on site). This further increases the costs.
In special cases where a turbocharger is matched to an internal combustion engine, such as in emergency electricity generating units, where a rapidly responding turbocharger is required, the mass moment of inertia of the rotor is reduced by employing an appropriate rotor in a lower mass material, for example, ceramic. These known rotors, however, are very expensive and, furthermore, do not have sufficient functional reliability.