Effect of Design Features on Dynamic Characteristics of VCC Piston for I. C. Engine 2013-01-0296
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.
By means of ADAMS dynamic simulation, the affecting factors on the dynamic characteristics of VCC piston, including stiffness, friction, damping, contacting conditions and engine working conditions, are investigated, and the effects of pre-tightening force and the design features on the dynamic response are also investigated.
The research indicates that (1) the dynamic response of VCC piston is very fast due to the design features of both ball-profiles and reset cam, and (2) by means of VCC displacement (the relative movement between the piston crown and the piston skirt), excessive in-cylinder pressure would be limited effectively in each working cycle while a spark-ignition engine running with higher CR (compression ratio), and (3) the dynamic response of VCC piston can be improved by reducing the pre-tightening force of the disc springs properly.