Many kinds of turbochargers have been mounted to engines for automotive use. Now, conventional, wastegated, variable geometry turbocharger and many systems are available. These turbocharged engines have many advantages, such as a high specific output power and good efficiency. Diesel engines are more suitable to turbocharging than spark ignition engines. But recently for a growing interest in acid rain and green house effect problems, regulations of engine exhaust gas emission have been tightened in Japan, USA and Europe. NOx and particulate matter from automotive engines must be reduced. In the USA, transient response of boost pressure has been important also for the EPA transient test mode. To cope with these regulations, diesel engine manufacturers demand turbocharger makers to provide far higher boost pressure than ever to supply more air to engines to improve combustion process. The requirements for turbocharger performance are wide operating range, high efficiency, and high specific-speed. Additionally, high pressure ratio also becomes important.
To satisfy these requirements, the new type of turbocharger series has been developed.
A compressor impeller for high pressure ratio was developed by reducing the impeller exit angle and increasing number of impeller blades. Air flow capacity of this new impeller was greater than conventional impeller by twenty percent at the same impeller tip diameter. Further, the rig test confirmed the reliability for low cycle fatigue life.
A mixed-flow turbine of small-diameter, light-weight and large swallowing-capacity was also developed. Stress analysis was proceeded on this new turbine impeller and housing.