A Study On Lubrication Performance Of Cylinder Liner-piston Ring Friction Pair

In the working process of the internal combustion engine,the friction loss is the main reason for the decrease of its work efficiency,and the piston ring-cylinder liner friction pair is one of the most important friction pairs in the internal combustion engine.The working conditions are harsh,and the friction loss is more,accounting for about26 % of the total friction loss.The lubrication performance of the piston ring-cylinder liner friction pair will directly affect the power,economy and service life of the internal combustion engine.In this thesis,a single cylinder diesel engine is taken as the research object.Considering the influence of engine operating conditions,cylinder liner deformation,surface roughness and surface texture,the lubrication performance of piston ringcylinder liner friction pair and its influencing factors are analyzed.The main research contents of this thesis are as follows :（1）The dynamic model of piston ring-cylinder liner friction pair and the thermodynamic model of diesel engine are established respectively.The combustion chamber pressure,temperature and heat transfer coefficient calculated by thermodynamic model are used as boundary conditions to calculate the thermalmechanical coupling deformation of the cylinder liner.The thermodynamic model calculation and cylinder liner deformation profile are introduced into the dynamic model of piston ring-cylinder liner friction pair to improve the data required for model calculation.According to the calculation results of the dynamic model,the overall lubrication performance of the piston ring-cylinder liner friction pair is analyzed,and the friction force and friction loss of the piston ring are mainly studied.The analysis results show that the fluid friction occurs throughout the cycle,which plays a leading role in the friction loss of the piston ring.However,the occurrence time of the asperity friction is less,which is mainly concentrated in the upper and lower stop points.The top ring in the piston ring group has the largest proportion in the total friction loss,followed by the third ring and the second ring,and the friction loss of the oil ring is the smallest.（2）Based on the dynamic model of piston ring-cylinder liner friction pair,the changes of surface roughness of cylinder liner and piston ring are analyzed respectively.The results show that the increase of the surface roughness of the cylinder liner will increase the total friction loss of the piston ring group,and the increase of the surface roughness of the piston ring will reduce the friction loss.The change of the surface roughness of the two has no effect on the sealing performance.The influence of the first three piston rings and the cylinder liner surface roughness on the average friction loss of the piston ring group was analyzed by the response surface method.The results show that the influence of the change of the cylinder liner surface roughness on the average friction loss is significantly stronger than that of the change of the piston ring surface roughness.（3）In addition to surface roughness,the influence of surface texture with different size parameters and positions on the lubrication performance of piston ring-cylinder liner friction pair was analyzed.The diameter,depth and location of the textured structure were analyzed and calculated,respectively.The results show that the average friction loss of the piston ring decreases first and then increases with the increase of the textured diameter,and the minimum value appears at the textured diameter of about500 μm.The effect of smaller texture depth on the average friction loss is obvious,and the trend of friction loss is relatively flat with the increase of depth.The position of texture has a significant effect on the average friction loss.When the texture appears in the middle of the piston ring surface,the average friction loss decreases significantly compared with other positions.（4）The texture parameters of the piston ring surface are optimized.The diameter,depth and distribution of the texture are selected as the design parameters.The neural network algorithm is used to optimize the multi-objective design with the minimum average friction loss as the design goal.The best combination of predicted parameters is: texture diameter 450μm,texture depth 20μm,middle position.The error between the neural network prediction results and the simulation results is 1.57 %,indicating that the neural network model is more accurate.