Technology for Improving Engine Performance using Variable Mechanisms

The concept of the Early or late Intake valve closing cycle has been examined over the years as a technique for improving fuel economy in conjunction with the use of a three-way catalyst for excellent exhaust emission performance. With this concept, the intake valve closing (IVC) timing is set either before or after bottom dead center. With the emergence of continuously variable valve timing and lift (VEL) systems in recent years, the Early IVC cycle has become a more familiar concept. However, the Early IVC cycle has an intrinsic drawback in that, although pumping losses decrease when charging efficiency is reduced in connection with IVC control, combustion performance deteriorates due to the decline in the effective compression ratio. In recent years, full-scale research has been undertaken on variable compression ratio systems as a new type of variable engine mechanism separate from variable valving.

This study examined the potential benefits of a new concept of high compression-expansion ratio combustion that combines these variable systems with the aim of obtaining functional synergies. In other words, a variable compression ratio mechanism is used to control the expansion ratio, and variable valving is used to control volumetric efficiency and the effective compression ratio. This paper describes the fuel economy and power output benefits obtained with this concept, based on the roles expected of the variable mechanisms. It also discusses issues that need to be addressed to further improve the performance expected from environmental engines.