OS-A4: A Study of a Variable Compression Ratio and Variable Valve Actuation System for Improving Fuel Economy(OS-A High Efficiency and Low Emission Engine by Variable Mechanism,Organized Session Papers)

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Variable engine mechanisms, such as variable compression ratio (VCR) and variable valve actuation (VVA) technologies, are being studied for improving fuel economy. The authors have developed a unique multiple-link VCR mechanism and a variable valve event and lift (VVEL) system as VVA mechanisms. This study examined the potential for improving fuel economy by using a system that combines both the multiple-link VCR and VVEL technologies. The multiple-link VCR mechanism achieves a longer piston stroke characteristic that resembles a simple sine curve. This unique long-stroke configuration suppresses the increase in the surface-to-volume (S/V) ratio of the combustion chamber as the compression ratio is raised, thereby avoiding an increase in the cooling loss. The VVEL system is effective in reducing the pumping loss by using the Miller-cycle under a low-load condition. In addition, the combination with the VCR mechanism expands the EGR limit by maintaining a higher effective compression ratio, resulting in reduced cooling loss. A prototype engine combining the long-stroke multiple-link VCR and VVEL systems was built and evaluated with regard to fuel economy. The results showed that fuel economy was improved by over 20% under a low-load condition through significant reductions of the cooling loss, exhaust loss and pumping loss.
2008-07-28