In recent years, the fuel efficiency of automobiles has been enhanced through the
supercharged downsizing of engines for passenger vehicles. To meet increasingly stricter fuel
efficiency regulations, however, turbochargers that have a wider operation range and are highly
efficient in comparison with existing ones are strongly required. For this reason, Mitsubishi Heavy
Industries, Ltd. (MHI) worked on the clarification of the internal flow phenomenon and design
improvement through large-scale flow analysis of the turbine in consideration of the engine
exhaust pulsation and visualization of the flow inside the compressor recirculation flow path, with
the purpose of enhancing the performance of the compressor and the turbine that govern the
performance of the turbocharger. In addition, a design optimization method was applied to plan a
concept to enhance the efficiency of the compressor impeller and execute design improvement of
the piping for a two-stage turbocharger. As a result, we enhanced the efficiency of a variable
capacity turbine at minimal flow, the efficiency of a twin-scroll turbine and the extension of the
operation range and efficiency of a compressor.
