Investigation Into The Dynamic Lubrication Modeling And Friction Measuring Between The Piston And Cylinder Liner

The friction and lubrication of piston-cylinder liner will directly influence the engine performance.Therefore,it is essential to carry out in-depth theoretical and experimental study on this friction pair to improve its lubrication condition and reduce the friction loss to improve the mechanical efficiency of the internal combustion engine.The researchers carried out a lot of theoretical research work,and more and more factors take into account the piston ring-cylinder liner lubrication model.While in previous studies of lubrication between piston rings and liner,most research was carried out based on a hypothesis that the inner surface of cylinder liner is an ideal cylindrical shell for simulation without taking the cylinder dynamic deformation effects on oil film lubrication into consideration.Actually,under the excitations of piston slap,the dynamic deformation of cylinder liner may affect the friction and lubrication performance between the piston rings and cylinder assemblies,it is necessary to improve existing lubrication models for research.The correctness of the improved lubrication model needs to be verified by experiments to correct the selection of key modeling parameters.So a motored engine test bench for testing the friction of cylinder-piston assembly in diesel engine was developed in this paper.Through the established finite element simulation of the cylinder liner-piston assembly,the dynamic deformation of the inner surface was obtained by dynamic simulation,then introduced into the lubrication model after processing to improve the existing lubrication model.By comparing the numerical simulation with the experimental results,the rationality of the improved lubrication model is analyzed and verified.In this thesis,the finite element model of cylinder liner is established in ANSYS software firstly.It carries out modal analysis in free state and obtains the modal information of cylinder liner.At the same time,the cylinder liner is tested in experimental modal testing.Comparing the simulation modal information,which verify the rationality of modeling methods and parameter selection.After that,constraint conditions were imposed on the floating liner device,and its modal information was obtained through simulation modal analysis,which laid the foundation for subsequent research.Secondly,the finite element model of cylinder liner-piston assembly was established in ANSYS software.The analytic calculation results of the piston side impact force were applied to the model.Through the transient dynamics analysis,the dynamic response of the cylinder liner under three test speeds was obtained.Then,the dynamic deformation of the inner surface is obtained by dynamic simulation is processed into the lubrication model.The effects of surface deformation on oil film thickness distribution and the oil shear characteristics are mainly considered.The influence of cylinder liner dynamic deformation on the friction and lubrication performance of the cylinder-piston ring lubrication system was analyzed.Based on the improved piston rings-cylinder liner lubrication model,the minimum oil film thickness and friction force curves are obtained by computation throughout the entire work cycle.The results indicate that,the minimum oil film thickness and the friction force obtained from the improved model manifests some obvious fluctuations,and shows a significant reduction.Finally,a series of motoring tests were carried out based on the built friction testing machine.The curves of friction force and side-thrust force of the piston ring-cylinder assembly under different speeds were obtained through motoring test.The time-frequency analysis of test data is carried out with continuous wavelet transform.The results show that the frictional fluctuations are related to the structural modal characteristics.By comparing friction force and side-thrust force curves obtained from the test and simulation,which can find that the trend of them can be well matched,so the rationality of the improved model is verified.The lubrication modeling and friction measurement methods proposed in this paper provide theoretical basis and practical guidance for the research and structural design of frictional lubrication behavior between piston ring and cylinder liner friction pair.