To address global warming as well as other environmental issues, emission restrictions across the world have gotten more rigorous, and the development of gasoline engines that are less damaging to the environment is progressing. Diesel engines are more effective than gasoline engines in terms of thermal efficiency, fuel economy, and CO2 emissions. In Europe, the proportion of automobiles powered by diesel engines as a proportion of all passenger cars has surpassed 50%. Turbochargers are commonly found in diesel engines, and they enhance diesel engine efficiency. Variable Geometry System (VGS) turbochargers have mostly replaced traditional wastegate turbochargers. There is a significant need to enhance the power density of turbochargers while increasing their performance and durability to improve engine fuel economy.
To stay competitive in the worldwide turbocharger industry, we created a new VGS turbocharger with increased turbine performance and reliability and began commercial production in real engines. This article covers the main technologies that have been adapted for the new VGS turbocharger, such as an enhanced VGS structure, a new manufacturing process, and a new material.
structure of VGS turbocharger
A turbocharger is a machine that activates high-pressure air for the engine using a rotating compressor driven by a coaxial turbine powered by flue gases.
VGS turbochargers may adjust supercharging pressure and engine exhaust pressure by opening and shutting the nozzle vanes to enhance the rate of Exhaust Gas Recirculation, allowing nitrogen oxide production to be controlled. When the engine is slowing down and there is minimal gas flow, the nozzles are closed to increase the flowrate of the gas reaching the turbine wheel. This raises the turbo rotation speed, which improves the engine’s transient response. With its outstanding endurance and transient properties, this structure can decrease the sliding friction load produced by opening and shutting the nozzles and assure smooth operation.
Improvement of turbine performance
Losses, such as the secession that occurs inside the turbine wheel as a result of clearance flows, which are mostly composed of radial velocity profile and infiltrate through the gaps between the nozzle vanes and the sliding surface, have a major influence on performance. These losses are regarded as the major reasons for turbine performance degradation. To keep the losses at the nozzle side clearances under control. To improve turbine performance, an unique nozzle vane with small nozzles and a long chord was fitted. Clearance has less of an impact on its performance variants. The nozzle vanes’ revised form was accomplished by utilising Metal Injection Molding (MIM) to enhance the general productivity.
MIM technique
Thin and complex three-dimensional components, such as nozzles, may now be produced using the MIM process, thanks to the maturation of mature, high-precision technologies in recent years.
MIM is a technique of manufacturing metal components that involves mixing metal powders with resin binders, putting the resulting liquid combination into a mould, extracting the resin material from the moulded parts by heating or chemical treatment, and finally sintering the parts. Mould injection of this type allows for the production of high-precision components. IHI Turbo’s MIM technology, which is presently being used, is very accurate and allows for manufacture without machining. It is now feasible to produce lighter weight components using this MIM method. This weight reduction should enhance resistance to abrasion induced by engine vibration.
MIM material evaluation
Sintered components with low filling factors have low mechanical strength; there is also an issue about oxidation breaking in the high-temperature gas environment. As a result, they were traditionally not utilised in turbochargers. However, the MIM method used allows for a high filling factor of 95 percent or more.
Tensile, fatigue, creep, and other types of strength assessment tests were performed on samples cut from real components to validate this process, and it was proven that the MIM material had strength equivalent to or greater than that of forging.
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