A theoretical study of the mechanism with variable compression ratio and expansion ratio

In recent years, due to global energy crisis, many governments have reduced emission of carbon dioxide by regulations, which make improving e?ciency of engines an important topic. Carmakers have focused on an energy-saving measure called variable compression ratio (VCR) because it suits related technologies with high e?ciency easily. Among numerous VCR mechanisms, one with eccentric sleeve should draw people’s attention, because it could vary both compression ratio and expansion ratio simultaneously, and also bring excellent energy-saving performance with Atkinson effect, which make the mechanism a rather promising measure in fuel reduction. This paper presents a theoretical study of the mechanism piston movement process, then a discussion about effects of the eccentric phase and bore-to-stroke ratio. The result shows that the mechanism has similar piston movement processes with conventional engines. A proper eccentric phase and a lower bore-to-stroke ratio are suitable to the mechanism because of a larger VCR range and enhanced Atkinson effect. The conclusion could be a necessary reference for the original dimension selection and quite essential to further improve the competitiveness of the mechanism.