Study On The Influence Of Piston Pin Offset On The Performance Of High-Power Diesel Engine

With the continuous development of diesel engines,high power,high rotational speed,and low energy consumption have become the development direction of the industry.Problems such as noise caused by cylinder knocking in the piston group,piston ring wear caused by poor lubrication conditions,and excessive consumption of lubricating oil need to be improved urgently.Piston pin biasing can make the piston in a tilted state during reversing,achieving early reversing,changing the effect of piston side thrust on the piston from a transient transition to a step-by-step transition,which can effectively reduce cylinder knocking.However,the impact on piston group dynamics,piston ring group lubrication characteristics,and piston group lubricating oil consumption is unknown.Therefore,based on piston pin dynamics theory,piston ring lubrication theory,and lubricating oil consumption mechanism,and considering the surface morphology and elastic deformation of the piston group,a single cylinder simulation model was established using AVL-Piston&Rings software to analyze the impact of piston pin offset direction and amount on piston group dynamics,piston ring lubrication characteristics,and piston group lubricating oil consumption.The main research contents include:(1)The dynamic characteristics and modeling method of piston group are studied.Firstly,the piston stiffness is analyzed and the piston stiffness matrix is obtained;Secondly,the cylinder pressure and heat transfer coefficient were obtained using AVL-Boost,and the heat transfer boundary conditions in each region of the temperature field of the piston and cylinder liner were calculated;Then,the thermal deformation of the piston and cylinder liner is calculated by finite element method to obtain the thermal profile.Finally,a model of the piston and cylinder liner is established.(2)The influence of piston pin offset on piston group mechanics was studied.Based on the piston group dynamics calculation theory,the impact on the dynamic characteristics of the piston group is analyzed by setting the displacement direction and amount of the piston pin.The results show that the offset should not exceed 2.1 mm.After the piston pin is biased,all state indicators of piston dynamics are improved,and the radial and torsional motions of each ring are improved.However,in contrast,after the piston pin is biased negatively,the piston knock decreases significantly;For the radial and torsional movements of the piston ring group,the positive deviation of the piston pin has a better improvement effect than the negative deviation of the piston pin.(3)The influence of piston pin offset on the lubrication characteristics of piston ring group was studied.Based on the piston ring lubrication theory,the influence of different distances between positive and negative piston pin deflections on the lubrication characteristics of piston ring groups was analyzed.The results show that the piston pin offset direction and distance have an impact on the lubrication characteristics of the piston ring group.When the piston pin is offset towards the secondary thrust side,the minimum oil film thickness between the ring group and the cylinder sleeve increases,the total friction loss decreases,and the maximum oil film pressure decreases overall;When the piston pin is biased towards the main thrust side,the minimum oil film thickness is greatly increased,the total friction loss is generally reduced,and the maximum oil film pressure is also greatly improved.After the negative deviation of the piston pin,various evaluation indicators are better than the positive deviation.(4)The influence of piston pin offset on the lubricating oil consumption characteristics of piston group was studied.Based on the theory of lubricating oil consumption,the influence of piston pin offset on lubricating oil consumption was analyzed with the piston pin offset direction and offset distance as independent variables.The results show that piston pin biasing can effectively reduce lubricant consumption.When the piston pin is offset,the cylinder wall evaporation decreases by 15.71%,the oil leakage in the closed gap decreases by 8.02%,the top ring oil rejection decreases by 97.85%,and the total lubricating oil consumption decreases by 13.17%;When the piston pin is biased negatively,the cylinder wall evaporation decreases by 16.83%,the oil leakage in the closed gap decreases by 13.18%,the top ring oil rejection decreases by 97.15%,and the total lubricating oil consumption decreases by 16.92%.Therefore,all indicators of lubricating oil consumption after negative piston pin deviation are better than positive piston pin deviation.