Abstract
In the in-line four-cylinder engine, it is well known that the shaking force is due to the vertical second harmonic acceleration components of the pistons. This paper proposes a kinematic conceptual design method to determine the kinematic structure of a feasible in-line four-cylinder variable compression ratio (VCR) engine and its dimensions that would yield a lower vertical second harmonic acceleration at joints. Through type and dimensional synthesis, candidate VCR engine mechanisms are chosen and their dimensions satisfying design specifications are determined. Based on the analysis of the vertical second harmonic acceleration components at the joints, a feasible mechanism for an in-line four-cylinder VCR engine is selected. Then, the method finds the dimensions that yield a nearly minimized sum of the vertical second harmonic acceleration at each joint by adjusting the link lengths within specified tolerances. For validation, the result is compared with that of a constrained optimization using MATLAB. The proposed method would be useful at the conceptual design stage of multi-link multi-cylinder VCR and variable-stroke engine mechanisms where the second harmonic acceleration is an important design factor in the automotive industrial applications.
Highlights
The general performance and thermal efficiency of the internal combustion engine have been improved by various technologies such as turbochargers, fuel injection systems, and variable valve actuation systems [1]
This paper proposed a kinematic conceptual design process of variable compression ratio (VCR) engine mechanisms considering the vertical second harmonic acceleration
From the graphs of six-link kinematic chains, Watt II and Stephenson III linkages were selected as candidate VCR engine mechanisms, and their initial dimensions satisfying the prescribed design specifications were determined
Summary
The general performance and thermal efficiency of the internal combustion engine have been improved by various technologies such as turbochargers, fuel injection systems, and variable valve actuation systems [1]. As the VCR engine mechanism has more links than the conventional fixed compression ratio engine, the design of a VCR engine mechanism could be a quite complicated problem: the kinematic structure and dimensions of the mechanism that fits within the internal space of the engine must be determined, and the dynamic characteristics and the balancing of shaking force and shaking moment need to be considered. The latter problem on the balancing of the conventional engine has been studied extensively [15,16,17].
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