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VCC (variable combustion chamber) piston technology would be one of the best substitutes for VCR (variable compression ratio) technology due to its extremely fast dynamic response with simple structure. One of the key issues of VCC piston technology is its dynamic response, which means fast, timely and enough variation of the combustion chamber volume during combustion in each working cycle while excess in-cylinder pressure occurs. Two key design features, ball-profiles and a reset cam, are introduced in order to ensure the availability of transient dynamic characteristics of VCC piston. Several formulas are derived from the structural analysis on VCC piston to describe the relationship between VCC piston design and its dynamic characteristics.

A patented VCC (variable combustion chamber) piston mechanism is presented, by which excess in-cylinder pressure would be able to be limited effectively based on each working cycle while a spark-ignition engine running with higher CR (compression ratio) of 12.0:1. A conventional engine can be converted to a VCC engine just by replacing its typical pistons with VCC pistons. Besides the benefits that VCR (Variable Compression Ratio) has been still pursued so far, there would be other advantages for VCC engine, such as excellent fuel economy at each load not only at light loads, and the improvement of cycle-by-cycle variation of in-cylinder pressure, and high reliability with simple structure. The innovative design of VCC piston is introduced. The main design features of VCC piston are a VCC mechanism assembled between the piston crown and the piston skirt, and a special reset cam assembled at the wrist-pin end of the connecting rod.