An exhaust manifold is used as the inlet area of an exhaust system and merges the separate exhaust gas streams usually coming from a plurality of combustion chambers of the internal combustion engine. An exhaust manifold usually comprises for this an engine flange, with which the exhaust manifold can be fastened to an engine block of the internal combustion engine. Separate inlet openings, which are associated with the individual combustion chambers of the internal combustion engine, are, in turn, provided in the area of the engine flange. The exhaust manifold is usually connected permanently with a turbine flange on the discharge side in a supercharged internal combustion engine in order to feed the exhaust gases arriving from the internal combustion engine to the turbine as close to the engine as possible. Double-flow turbines, so-called twin-scroll turbines, may be used in internal combustion engines that have two cylinder banks or two groups of cylinders. To prevent the two cylinder groups from mutually interacting with one another, the exhaust gas is likewise routed in two flows up to the double-flow turbine, so that the exhaust manifold has separate manifolds for the two cylinder groups, which said manifolds lead each from a plurality of inlet openings to an outlet opening, and the two outlet openings of the separate manifolds feed the separate exhaust gas streams to separate inlet openings of the turbine in the turbine flange.
It is known that such an exhaust manifold can be equipped with an air gap insulation for improved heat insulation. This is achieved by an exhaust gas-carrying inner pipe being enveloped by an outer pipe, forming a gap, and this gap between the inner pipe and the outer pipe forms the desired air gap insulation. The outer pipe and inner pipe may also be called outer shell and inner shell, respectively.
For a supercharged internal combustion engine with twin-scroll turbine, an air gap-insulated exhaust manifold thus comprises an engine flange for fastening the exhaust manifold to the engine block of the internal combustion engine, a turbine flange for fastening the exhaust manifold to the turbine of the exhaust gas turbocharger, two separate inner pipes, which lead each from at least one inlet opening for exhaust gas arranged in the area of the engine flange to an outlet opening for exhaust gas arranged in the area of the turbine flange, as well as an outer pipe, which envelops the two inner pipes, forming an air gap insulation and extends essentially from the engine flange to the turbine flange.
The inner pipes may have a multipart design in order to make it possible to merge a plurality of inlet openings into a common outlet opening in a simpler manner. The individual members of the respective inner pipe may be inserted one into another to make relative motions caused by thermal effects possible. Leaks may develop due to these plug-type connections, as a result of which exhaust gas can escape from the respective inner pipe and enter the interior space of the outer pipe, which said interior space is enveloped by the outer pipe. Such tolerable leaks occur in a pulsed manner, corresponding to the working rhythm of the internal combustion engine. To prevent these pressure pulsations of the two cylinder groups within the exhaust manifold from mutually affecting each other, a partition, which divides the interior space of the outer pipe into two interior spaces, in which one of the two inner pipes each is arranged, may be arranged in the outer pipe. This partition advantageously extends from the turbine flange to the engine flange.
It was found that such a partition is subject to very high thermal loads because of it being positioned between the two inner pipes. In particular, the partition is subject to strong thermal expansion effects. Undesired wear may develop as a result.