Abstract
Research and/or Engineering Questions/Objective
Rising interest in automotive exhaust gas problems has triggered the active study on eco-friendly automobiles. Variable compression ratio (VCR) engine is among one of those eco-friendly car technologies. VCR increases the compression ratio at the low load region to improve thermal efficiency, while it decreases the compression ratio in the high load region to preventing knocking, which can decrease exhaust emissions and increase fuel-economy. In this paper, a new variable compression ratio engine mechanism is developed via a systematic approach.
Methodology
In order to establish a new mechanism, the number of links and joints is determined through degree of freedom equation. Based on the determined number of links and joints, available graphs are enumerated by using graph theory. Then, specific roles are assigned to links and joints to meet the conditions of the design. Finally, a dimensional synthesis is applied to determine the dimensions of the mechanism which fulfills requirements for movement.
Results
Through graph theory and degree of freedom equation, graphs of feasible mechanisms for variable compression ratio engine mechanisms are enumerated. Based on these enumerated graphs, a new variable compression ratio engine mechanism is determined.
Limitations of this study
Since a variable compression ratio engine mechanism is larger than the conventional non VCR engine in general, the engine block must be more spacious to provide enough space for the mechanism. Therefore, to build a variable compression ratio engine, a new engine block must be designed.
What does the paper offer that is new in the field including in comparison to other work by the authors?
This paper takes a step forward from the past studies of the authors which are limited to enumeration of graphs from existing variable compression ratio engine mechanisms. This paper aims to develop a new variable compression ratio engine via a systematic approach.
Conclusions
Feasible graphs of variable compression ratio engine mechanisms are enumerated through degree of freedom equations and graph theory. Based on the finding, the most appropriate graph is selected for the variable compression ratio engine mechanism. Finally, a new variable compression ratio engine is proposed.
Key Words : Degree of freedom; Graph theory; Variable compression ratio engine;