Research and development of new variable compression ratio (VCR) engine mechanism (1st report, Basic characteristics and design of VCR engine mechanism)

Abstract

In order to improve the efficiency of combustion engines, variable compression ratio (VCR) engine is researched. VCR engine changes the compression ratio according to its mechanical configuration. One of the solutions to construct VCR engine is the multi-link type. Multi-link type has an advantage for reducing high order shaking force which is the source of mechanical vibration. Since piston motion strongly influences shaking force, it is required to make the piston displacement profile close to sine curve. However, conventional combustion engine is designed based on four-link piston crank mechanism. Because of the design constraint due to four-design parameters regarding the four-link piston crank mechanism, piston displacement profile diverges from sine curve. In order to solve this problem, six-link piston crank mechanism is applied to VCR engine. Since six-link piston crank mechanism has six-design parameters, the piston displacement profile becomes closer to sine curve than that of the four-link piston crank mechanism. A Stephenson type six-link piston crank mechanism whose constitute four-bar mechanism is the double-crank mechanism is newly designed. Basic characteristics of VCR engine model, that includes the piston displacement profile and its similarity for sine-curve, and peak acceleration amplitude with respect to different compression ratio, was researched based on kinematic analysis. The obtained theoretical results are compared with experimental ones. As a result, experimental values almost agree with theoretical values.