Research On The Multi-scale Mixed Lubrication Model For The Cylinder Liner-piston Ring Pack And Prediction Method Of Surface Topography Evolution

The cylinder liner-piston ring system is the key friction pair of an internal combustion engine,which is very important to realize the goal of energy saving and emission reduction.All the time,it has received extensive attention from both academic and industrial circles.Furthermore,during the operation of the engine,the cylinder liner surface topography and the tribological properties of the system are in dynamic evolution process owing to running in and wear.Severe wear may lead to the occurrence of the scuffing.Therefore,it is of great significance to study the evolution of the cylinder liner surface topography.In this paper,a two-scale homogenized mixed lubrication model is firstly developed according to the multi-scale characteristics of the contact interface between the cylinder liner and the piston ring.In the model,the cylinder liner surface is decomposed into the plateau roughness and the valley component(cross-hatched texture)based on the mathematical morphology.Thus,the plateau roughness is considered on the local scale,and the valley component is considered on the global scale.Then,under starved lubrication and the cylinder deformation conditions,the performance of the piston ring-pack is investigated.Then,a two-scale wear model is developed.Based on the coupling analysis of the wear process and the mixed lubrication process,the evolution of the cylinder liner surface topography and the tribological properties of the system are simulated and verified by experiments.Finally,after analyzing the influence of the cylinder surface topography on the tribological performance of the cylinder liner-piston ring system,two improved cylinder liners were designed and proposed for a diesel engine.The two improved cylinder liners and the original cylinder liner are compared by conducting simulation analysis,and the simulation results are also verified by experiments.The main contents are as follows:(1)The construction process of the two-scale homogenized mixed lubrication model of the cylinder liner-piston ring system is introduced in detail.The kinematics and dynamics models of the piston ring and the leakage model of the piston ring-pack are introduced firstly.Then,based on the mathematical morphology method,how to separate the plateau roughness and the valley component is introduced.In the model,the plateau roughness is considered on the local scale,and the valley component is considered on the global scale in order to predict the lubrication performance more accurately,Then,the derivation and efficient numerical solution of the one-dimensional and two-dimensional homogenized Reynolds equations are introduced in detail,and the corresponding efficient methods for solving one-dimensional and two-dimensional deterministic asperity contact models are also presented.(2)Based on the developed two-dimensional two-scale mass-conserving homogenized mixed lubrication model,the effects of the multi-scale charateristics of the friction pair interface under starved lubrication and the cylinder deformation conditions are investigated.A new efficient flow continuity lubrication model for the piston ring-pack is established by taking the oil storage of the cross-hatched texture into account.The oil available to lubricate each ring is determined by conducting an oil transport analysis.The trapped oil in the texture is calculated as an extra oil supply to the inlet of the contact.The developed model has great potential for understanding and optimizing the honed cylinder liner surface.When the multi-scale characteristics of the interface and the deformation of the cylinder liner are considerd at the same time,a major problem is the huge amount of calculation.After analyzing the cylinder liner deformation and the piston ring conformability,the effect of four order deformation of cylinder liner is considered for the time being.Therefore,only 1/8 region in the circumferential direction is chosen as the solution domain in order to reduce the calculation costs.Symmetry boundary condition is used at the edges in the circumferential direction.(3)A two-scale wear model is established to study the evolution of the cylinder liner surface topography.The two-scale homogenized mixed model is used to characterize the lubrication properties and the contact severity of the cylinder liner-piston ring system.On this basis,the evolution of the cylinder liner surface topography is divided into two stages: at the first stage,running-in of the plateau component on the local scale;at the second stage,wear of the valley component on the global scale.On the local scale,the influence of the plateau component running-in on the homogenized flow factors and contact stiffness is studied.On the global scale,the influence of the valley component wear on the lubrication properties(load carrying capacity,contact force and friction coefficient)is studied.The two-scale model is verified by conducting experiments on both a reciprocating tester and a real engine.(4)Based on the one-dimensional two-scale homogenized mixed lubrication model,the influence of the cylinder liner surface topography on the tribological performance of the cylinder liner-piston ring system is investigated.The influence of engine condition and ring profile on low friction design of the cylinder liner surface topography is studied,which provides an important reference for the low friction design.After that,two improved liners are designed and proposed on the basis.The two improved cylinder liners and the original cylinder liner are compared by conducting simulation analysis,and the simulation results are also verified by experiments.