Kinematic Conceptual Design of In-Line Four-Cylinder Variable Compression Ratio Engine Mechanisms Considering Vertical Second Harmonic Acceleration

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.

Type Synthesis of Variable Compression Ratio Engine Mechanisms

“…mechanism. Kwak et al [14] proposed a kinematic conceptual design procedure for in-line fourcylinder VCR engine mechanisms considering vertical second harmonic acceleration. The compression ratio of the VCR engine can be modified by moving or tilting the cylinder head, moving the crankshaft axis, varying the piston deck height or the combustion chamber volume, moving the crankpin, or modifying the connecting rod geometry using a control linkage system [1,15,16].…”

“…After enumerating contracted graphs with l c vertices and j c edges given by Equations (14) and (15), the edges in the contracted graphs need to be replaced by binary strings to determine conventional graphs. Let a binary string of length i in a conventional graph be defined as a string of i vertices of degree two connected in series by i + 1 edges between nonbinary vertices.…”

“…Besides the difficulties in the dimensional synthesis of 2-DOF mechanisms, the same kinematic structure may have completely different kinematic and dynamic characteristics depending on the dimensions and pivot positions of implemented mechanisms. For example, Kwak et al [14] showed that by adjusting the link lengths and pivot position of an initially designed Stephenson III VCR engine mechanism within prescribed…”

“…Among the literature on the kinematic structures of VCR engines [6][7][8][9][10][11][12][13][14][15][16][17][18], Freudenstein and Maki [6] applied a systematic search procedure for the type synthesis of one-degree-of-freedom (DOF) variable-stroke IC engine mechanisms and enumerated 39 kinematic structures with six and eight links, and then determined three potentially acceptable mechanisms by evaluating the enumerated structures. H. N. Pouliot et al [7] developed a nine-link variable-displacement engine and obtained data on power, fuel consumption, and emission with engine dynamometer tests.…”

“…Cassiani et al [13] analyzed the kinematic and dynamic model of the Saab Variable Compression (SVC) engine mechanism. Kwak et al [14] proposed a kinematic conceptual design procedure for in-line four-cylinder VCR engine mechanisms considering vertical second harmonic acceleration.…”