Analysis On The Performance Of The Textured Internal Combustion Engine Critical Friction Pairs Under The Mixed Lubrication Regime And Research On The Involved Friction Reducing Mechanism

The internal combustion engine is the main power plant of automobiles and ships.Reducing the friction loss of the critical friction pairs in the engine and improving the engine economy have been regarded as the pursuits of the practitioners in this field.Both the piston ring/cylinder liner system and the crankshaft/main bearing system are two critical friction pairs of the internal combustion engine.The mechanical power loss of these two systems accounts for a large proportion of the overall mechanical loss of the engine.It has the great application value to perform the low-friction design about these two systems.As an important method to improve the lubrication performance,surface texturing has attracted much attention of researchers in recent years.However,most of the studies involving the textured lubrication tribological systems only focused on the assumed steady state.The studies based on the actual engine conditions were very lack.Therefore,it is difficult to provide the reliable theoretical support for the application of surface texturing in the engine.Therefore,this thesis will emphatically study the effect of surface texturing on the performance improvement of the critical friction pairs of internal combustion engines,thus laying a foundation for the low friction design of internal combustion engine friction pairs.In this thesis,researching the lubrication theory of the textured system is carried out.A mixed lubrication model is developed to study the textured system.The piston ring/cylinder liner system and crankshaft/journal bearing system were used as the research objects.The tribological properties of the textured systems under the cold and warm engine like conditions were studied.The performances of textured systems in the start-up stage were predicted under the fully flooded and starved lubrications.The variation of surface topography during the running-in stage of ring/liner system was analyzed.The main contributions are given as follows:Firstly,based on the mass conservation lubrication model and asperity contact model,a mixed lubrication model was established after considering the rheological properties of lubricant and the influence of surface roughness on lubrication flow.In the developed model,the texture scale and macro scale were accurately characterized by numerical reconstruction,while the roughness scale was characterized by the statistical method.The model is especially suitable for the textured lubrication system.Meanwhile,the fast solution of this model was given by adopting FBNS(Fischer-BurmeisterNewton-Schur)algorithm.Using this model,the effects of surface texturing in different lubrication regimes were analyzed,as well as the influences of surface texturing on the transmit of lubrication regimes.This work lays a theoretical foundation for the following research.Secondly,the piston ring/cylinder liner system was used as the object of study.The tribological performances of textured piston ring/cylinder liner under the cold and warm engine conditions were investigated,as well as its performances under the cold startingup engine condition.One thermal mixed lubrication model was developed for the ring/ liner system,in which the thermal effect of lubrication was studied by the improved energy equation with the effect of surface roughness in consideration.It was found that the friction reduction effect of surface texturing can reach 6%-15% in the given texturing case.In the simulation of start-up conditions,the application of surface texturing can reduce the power loss by 8% at the start-up stage.Thirdly,based on the flow conservation equations at the inlet region,the starved lubrication models considering the effect of surface texturing were established for the textured systems.The starved lubrication models can be divided into two kinds: one is for the stationary texture;another is for the moving texture.For the ring/liner system,the two kinds of starved lubrication models are suitable for sloving the lubrication problems for the textured ring system and the textured liner system,respectively.The performances of surface texturing in the normal start-up process were studied under the fully flooded/starved lubrication condictions.The effects of textures in the start-up process were analyzed.Meanwhile,by combining the mixed lubrication model with the wear model,a prediction model was developed to predict the tribological behaviors of piston ring/cylinder liner systems under the running-in stage.In the mixed lubrication wear model,the asperity plastic deformation and the evolution of the asperity height distribution were considered.Based on the mixed lubrication wear model,the behavior of piston ring/cylinder liner system during the running-in stage was successfully investigated.The results show that the change of asperity height distribution induced by asperity plastic deformation is remarkable in the initial stage of running-in process.The contribution of asperity plastic deformation on the surface smoothing should also be considered,particularly in the initial stage of running-in process.Finally,the crankshaft/journal bearing system was also used as the object of the study.The influence of the texturing distribution on the tribological properties of journal bearing system was studied.The effects of surface texturing on the performance of the bearing systems at the start-up stage were also analyzed.Meanwhile,a mixed lubrication model with the effects of macro cavitation and micro cavitation in consideration was also established.In the developed mixed lubrication model,the microscopic cavitation effect caused by random surface roughness was considered by the statistical means.The results show that the effects of surface texturing on the bearing systems can be positive or negative.With the increase of engine speed,the friction reduction effect induced by surface texturing will change from negative to positive.In the given texturing cases,the friction reduction effect induced by surface texturing can reach 12%(at 6000 RPM(revolutions per minute)),while the textured system does not have the ideal tribological properties when at low speed.