Simulation Research On The Loosening Of Connecting Rod Small End Bush Considering Mixed Lubrication

Connecting rod small end bush is one of the important parts of the diesel engine. Withthe continuous strengthening of the diesel engine, the lubricating condition of piston pinbearing becomes more severe, which may result in unexpectedly rotation, loose or evenserious ablation. Therefore, researching on the loose of small end bush is significant toimprove the reliability of the piston pin bearing. In order to solve the problem of small endbush loosening in the highly-intensified diesel engine, the flexible multi-body dynamicsmodel of piston-connecting rod system and the thermal elastic-plastic finite element modelof small end bush were established, and thus the lubrication characteristics of the floatingpiston pin and loosening mechanism of small end bush were analyzed, and then themeasurements to prevent the loose of small end bush was studied. The main contents wereas follows:1) Based on the flexible multi-body dynamics theory, EHL theory, the average flowmodel and asperity contact theory, the flexible multi-body dynamics model of thepiston-connecting rod system in single-cylinder in-line diesel engine was established, andthe elastic deformation, and the surface roughness of piston pin, small end bush and pistonpin hole were considered. Then the movement characteristics of floating piston pin and themixed lubrication characteristics of floating piston pin bearing were analyzed.2) Based on the pressure load distribution on inner surface of small end bush and thethermal load distribution of piston pin bearing, the thermal elastic-plastic finite elementmodel of small end bush was established, and the loosening situation of small end bush inthe three dangerous working conditions were analyzed, and then the effects of the thermalload of piston pin bearing and the interference between small end bush and connecting rodon the loosening of small end bush were also analyzed. The loosening mechanism of smallend bush was described.3) Based on the flexible multi-body dynamics model of piston-connecting rod system,the effects of the working parameters (i.e. the maximum slope of the connecting rod journal,gas pressure, engine speed, and the dry friction resulted from the lack of oil) and the structure parameters (i.e. the profile line of small end bush, the surface roughness, and thebearing clearance) of piston pin joint on the friction power loss of piston pin bearing wereanalyzed. The measures to prevent the loose of small end bush were presented.