Method for manufacturing multistage exhaust turbocharger

1. A method of manufacturing a multistage exhaust turbocharger for an internal combustion engine, the multistage exhaust turbocharger including a high-pressure stage turbocharger having a high-pressure turbine drivable by exhaust gas from an exhaust manifold of the engine, and a low-pressure stage turbocharger having a low-pressure turbine drivable by exhaust gas flowed out from the high-pressure turbine after driving the high-pressure turbine, said method comprising:

providing a high-pressure turbine housing of the high-pressure stage turbocharger, the high-pressure turbine housing being integrally formed with the exhaust manifold by casting;

assembling constituent parts of the high-pressure stage turbocharger using the high-pressure turbine housing as a reference;

after said assembling constituent parts of the high-pressure stage turbocharger, attaching the low-pressure stage turbocharger to the high-pressure stage turbocharger by attaching a low-pressure turbine housing to a low-pressure turbine connection flange provided at an exhaust outlet side of the high-pressure stage turbocharger; and

after said attaching the low-pressure stage turbocharger, attaching an air supply channel to connect between a supply air outlet of the low-pressure stage turbocharger and a supply air inlet of the high-pressure stage turbocharger,

wherein the high-pressure stage turbocharger has a rotation axis,

wherein the low-pressure stage turbocharger is disposed below the high-pressure stage turbocharger when viewed in a direction parallel to the rotation axis of the high-pressure stage turbocharger,

wherein the high-pressure stage turbocharger and the low-pressure stage turbocharger are arranged sequentially in the flow path of the exhaust gas of the engine,

wherein the high-pressure stage turbocharger has a high-pressure compressor and the low-pressure stage turbocharger has a low-pressure compressor, and

wherein the air supply channel supplies supply air for the engine pressurized by the low-pressure compressor to the high-pressure compressor to be further pressurized by the high-pressure compressor.

2. The method of claim 1 , wherein the high-pressure stage turbocharger includes:

a high-pressure compressor cover accommodating the high-pressure compressor, the high-pressure compressor cover including the supply air inlet of the high-pressure stage turbocharger;

an exhaust gas guide member having a low-pressure turbine connection flange for connecting the high-pressure turbine housing and the low-pressure turbine housing; and

an exhaust gas outlet flange on the high-pressure turbine housing,

wherein the low-pressure stage turbocharger includes a low-pressure compressor cover accommodating the low-pressure compressor, the low-pressure compressor cover including the supply air outlet of the low-pressure stage turbocharger, and

wherein the exhaust gas guide member is attached to the exhaust gas outlet flange of the high-pressure turbine housing, then the low-pressure turbine housing is attached to the low-pressure turbine connection flange of the exhaust gas guide member, and then the air supply channel is attached between the supply air outlet of the low-pressure stage turbocharger and the supply air inlet of the high-pressure stage turbocharger.

3. The method of claim 1 , wherein the high-pressure stage turbocharger includes an exhaust gas guide member, and the low-pressure stage turbocharger is connected to the exhaust gas guide member,

wherein assembled at one side of the engine are the exhaust manifold formed integrally with the high-pressure turbine housing, the high-pressure stage turbocharger, and the low-pressure stage turbocharger, in order from the top side.

4. The method of claim 1 , wherein the high-pressure stage turbocharger and the high-pressure turbine housing are attached to the engine, and then the low-pressure stage turbocharger is attached to the high-pressure stage turbocharger.

5. The method of claim 1 , wherein the low-pressure stage turbocharger is disposed below the high-pressure stage turbocharger in a vertical direction which is perpendicular to the rotation axis of the high-pressure stage turbocharger.

6. The method of claim 1 , further comprising mounting the exhaust turbocharger at one side of the engine in a lateral direction of the engine with the rotation axis of the high-pressure stage turbocharger being parallel to the axial direction of the engine,

wherein the low-pressure stage turbocharger is disposed below the high-pressure stage turbocharger in a vertical direction of the engine which is perpendicular to the axial direction of the engine and perpendicular to the lateral direction of the engine.

7. The method of claim 1 , wherein the low-pressure stage turbocharger is disposed below the high-pressure stage turbocharger when viewed in an axial direction of the engine without the low-pressure stage turbocharger and the high-pressure stage turbocharger being on the same axis of the engine.

8. The method of claim 1 , wherein a rotation axis of the low-pressure stage turbocharger is offset from the rotation axis of the high-pressure stage turbocharger in a vertical direction perpendicular to the rotation axis of the high-pressure stage turbocharger.