Design and Kinematic Characterization of Connecting Rod Set for Variable Compression Ratio Engines

The aim of this study is to design and analyze a variable compression ratio (VCR) technology gasoline engine variable compression ratio connecting rod set and to verify its kinematic properties through numerical simulations. This study first constructs a mathematical model of the VCR connecting rod set and derives its kinematic equations. Numerical simulations were carried out using MATLAB R2022b software to analyze the kinematic state of the piston under different compression ratio conditions. The results show that the equations of motion of the VCR mechanism realize continuously variable compression ratios from 8 to 14, which provides a valuable reference for the study of overall engine performance control. This study also verified the accuracy of the theoretical model through the multibody dynamics software ADAMS 2020 to ensure the reliability of the model. The results of this study show that the piston position is jointly influenced by the crankshaft angle and the control shaft angle, and a change in the control shaft angle leads to a change in the piston upper and lower stop positions and stroke. With the increase in the control shaft angle, the maximum velocity (absolute value) of the piston gradually decreases, while the maximum acceleration (absolute value) gradually increases. The results of this study provide important reference data for the development of variable compression ratio engines.