Shafting Performance and Coordinated Design of Low-Speed Two Stroke Marine Engine

_ The bearing is a key component of an internal combustion engine, which is used to support the crankshaft system. Its lubrication performance and wear life will directly affect the working efficiency and reliability of the internal combustion engine. Among these, the crankshaft and engine bed deformation have an important impact on the bearing performance. Different stiffness and deformation between the crankshaft and bearing seat lead to bearing edge load and lubrication problems. Insufficient stiffness easily causes vibration, and on the contrary, too large stiffness leads to lubrication problems. Therefore, the research on bearing structure, crankshaft, and seat deformation matching for improving shafting stability and lubrication performance of main bearings is of great significance to improve the performance of the internal combustion engine. In this paper, a theoretical coupling model of multibody dynamics and elastohydrodynamic lubrication for a low-speed two-stroke diesel engine is established. The dynamic model was verified by the torsional vibration test. The factors affecting the coordinated deformation ability of crankshaft-bearing seats, including the stiffness of the whole engine and the clearance of the bearing, are selected to investigate the influence of these factors on the bending vibration of the crankshaft, bearing lubrication, and wear. The analysis shows that the lubrication performance of the seventh main bearing is the worst among the eight main bearings under the rated condition of the engine. The multiobjective optimization model optimizes the stiffness of each main bearing seat. The results show that the performance of the shaft can be improved by deformation-coordinated design. The thickness of the minimum oil film of the main bearing increases by 6.78%, the peak value of the maximum oil film pressure decreases by 16.64%, and the bending amplitude of the main journal decreases by 21.67%. The optimized result provides a solution for performance improvement on bearing lubrication and vibration of low-speed two-stroke engines. Keywords marine engine; EHD; main bearing; coordinated design