Engineering Transactions, 70, 1, pp. 3–22, 2022

Theoretical Study of the Motion Characteristics of a Variable Length Connecting Rod Mechanism

Jiadui CHEN
Guizhou University

Qinghua LIU
Guizhou University

Guizhou University

The sustainable development of society calls for automobile engines with high efficiency and very low pollutant emission. The variable compression ratio (VCR) technique is one of the effective methods to deal with this issue. Engines with variable length connecting rod (VLEs) yield higher efficiency than other VCR engines. This paper focuses on a variable length connecting rod mechanism that achieves a VCR by changing the positions of the bottom dead center (BDC) and the top dead center (TDC) (controlled by the rotation of the eccentric sleeve) relative to the crankshaft. A kinematic model is also proposed to calculate and analyze the motion characteristics of the variable length connecting rod mechanism. The effects of eccentric size and eccentric phase on the piston motion, the TDC and BDC positions, the stroke length, the crank angles at TDC and BDC, and the compression ratio are studied in detail. It is found that the piston exhibits good motion characteristics with proper eccentric size and eccentric phase, and the compression ratio can be adjusted by varying the eccentric phase with proper eccentric size. A comparison between the proposed mechanism with another mechanism is also conducted. Therefore, this work can serve as a necessary reference for designing, analyzing, and optimizing VLEs.
Keywords: variable length connecting rod engine; variable stroke; variable compression ratio; kinematic model; piston movement process
Full Text: PDF
Copyright © The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0).


Ganesan V., Internal Combustion Engines, McGraw Hill, India, 2012.

Hoeltgebaum T., Simoni R., Martins D., Reconfigurability of engines: A kinematic approach to variable compression ratio engines, Mechanism and Machine Theory, 96(Part 2): 308–322, 2016, doi: 10.1016/j.mechmachtheory.2015.10.003.

Heywood J., MacKenzie D. [Eds], On the road toward 2050: potential for substantial reductions in light-duty vehicle energy use and greenhouse gas emissions, Massachusetts Institute of Technology, pp. 301–313, 2015,

Feng D.Q., Wei H.Q., Pan M.Z., Comparative study on combined effects of cooled EGR with intake boosting and variable compression ratios on combustion and emissions improvement in a SI engine, Applied Thermal Engineering, 131: 192–200, 2018, doi: 10.1016/j.applthermaleng.2017.11.110.

Yang S., Lin J.S., A theoretical study of the mechanism with variable compression ratio and expansion ratio, Mechanics Based Design of Structures and Machines, 46(3): 267–284, 2018, doi: 10.1080/15397734.2017.1332526.

Westerloh M., Twenhövel S., Koehler J., Schumacher W., Worldwide electrical energy consumption of various HVAC systems in BEVs and their thermal management and assessment, SAE Technical Paper, 2018-01-1190, 2018, doi:10.4271/2018-01-1190.

Clenci A. C., Descombes G., Podevin P., Hara V., Some aspects concerning the combination of downsizing with turbocharging, variable compression ratio, and variable intake valve lift, Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 221(10): 1287–1294, 2007, doi:10.1243/09544070jauto449.

Mingfa Y., Zhaolei Z., Haifeng L., Progress and recent trends in homogeneous charge compression ignition (HCCI) engines, Progress in Energy and Combustion Science, 35(5): 398–437, 2009, doi: 10.1016/j.pecs.2009.05.001.

Hiyoshi R., Aoyama S., Takemura S., Ushijima K., Sugiyama T., A study of a multiple-link variable compression ratio system for improving engine performance, SAE Technical Paper, 2006-01-0616, 2006, doi: 10.4271/2006-01-0616.

Takahashi N., Aoyama S., Moteki K., Hiyoshi R., A study concerning the noise and vibration characteristics of an engine with multiple-link variable compression ratio mechanism, SAE Technical Paper, 2005-01-1134, 2005, doi: 10.4271/2005-01-1134.

Asthana S., Bansal S., Jaggi S., Kumar N., A comparative study of recent advancements in the field of variable compression ratio engine technology, SAE Technical Paper, 2016-01-0669, 2016, doi: 10.4271/2016-01-0669.

Mane P., Pendovski D., Sonnen S., Uhlmann A., Henaux D., Blum R., Sharma V., Coupled dynamic simulation of two stage Variable Compression Ratio (VCR) connecting rod using virtual dynamics, SAE International Journal of Advances and Current Practices in Mobility, 1(1): 38–44, 2019, doi: 10.4271/2019-26-0031.

Shelby M.H., Leone T.G., Byrd K.D., Wong F.K., Fuel economy potential of variable compression ratio for light duty vehicles, SAE International Journal of Engines, 10(3): 817-831, 2017, doi: 10.4271/2017-01-0639.

Kojima S., Kiga S., Moteki K., Takahashi E., Matsuoka K., Development of a new 2L gasoline VC-turbo engine with the world’s first variable compression ratio technology, SAE Technical Paper 2018-01-0371, 2018, doi: 10.4271/2018-01-0371.

Romero C., Henao Castañeda E. , Developing small variable compression ratio engines for teaching purposes in an undergraduate program, SAE Technical Paper 2019-01-0331, 2019, doi: 10.4271/2019-01-0331.

Shaik A., Moorthi N.S.V., Rudramoorthy R., Variable compression ratio engine: A future power plant for automobiles – an overview, Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 221(9): 1159–1168, 2007, doi: 10.1243/09544070JAUTO573.

Wittek K., Geiger F., Andert J., Martins M., Oliveira M., An overview of VCR technology and its effects on a turbocharged DI engine fueled with ethanol and gasoline, SAE Technical Paper 2017-36-0357, 2017, doi: 10.4271/2017-36-0357.

Shi H., Al Mudraa S., Johansson B., Variable compression ratio (VCR) piston – design study. SAE Technical Paper 2019-01-0243, 2019, doi: 10.4271/2019-01-0243.

Kadota M., Ishikawa S., Yamamoto K., Kato M., Kawajiri S., Advanced control system of variable compression ratio (VCR) engine with dual piston mechanism, SAE International Journal of Engines, 2(1): 1009–1018, 2009, doi: 10.4271/2009-01-1063.

Kleeberg H., Tomazic D., Dohmen J., Wittek K., Balazs A., Increasing efficiency in gasoline powertrains with a two-stage variable compression ratio (VCR) system, SAE Technical Paper 2013-01-0288, 2013, doi: 10.4271/2013-01-0288.

Yamin J.A.A., Ozcan H., Second-law analysis of an LPG-powered 4-stroke SI engine under variable stroke length and compression ratio, International Journal of Exergy, 8(2): 113–127, 2011, doi: 10.1504/IJEX.2011.038514.

Jiang S., Smith M.H. Geometric parameter design of a multiple-link mechanism for advantageous compression ratio and displacement characteristics, SAE Technical Paper 2014-01-1627, 2014, doi: 10.4271/2014-01-1627.

Rufino C.H., Ferreira J.V., Kinematics of a variable stroke and compression ratio mechanism of an internal combustion engine, Journal of the Brazilian Society of Mechanical Sciences and Engineering, 40: Article number: 476, 2018, doi: 10.1007/s40430-018-1396-x.

Chen J., Wang B., Liu D., Yang K., Study on the dynamic characteristics of a hydraulic continuous variable compression ratio system, Applied Sciences, 9(21): 4484, 2019, doi: 10.3390/app9214484.

DOI: 10.24423/EngTrans.1372.20220207