Dynamic Coupling Simulation Between The Lubrication And Wear Of The Main Bearing System For Low Viscosity Multi-cylinder Internal Combustion Engines

The simplest and most cost-effective way to reduce friction losses in internal combustion engines(ICE)is reducing the viscosity of the lubricant directly,however,the application of lowviscosity oils will lead to problems such as increased wear.Therefore it is,necessary to conduct a simulation study of the lubrication-wear dynamics of the main bearing system for low-friction multi-cylinder ICEs.In this paper,the operating characteristics of a multi-cylinder ICE with increased local total pressure and shear rate in the main bearing after the application of low-viscosity oils.A new model of non-linear lubricant viscosity was proposed considering the viscous pressure effect and shearthinning effect,and a transient lubrication simulation model of the main bearing system under a mixed lubrication regime was carried out for the application of the low-viscosity oil.A dynamic coupling simulation model for lubrication and wear of the main bearing system was developed,taking the wear evolution of the main bearing into account,and then an iterative wear profile method that balances calculation accuracy and efficiency was proposed.The dynamic coupling mechanism of lubrication and wear in the main bearing system was explored,and the sensitivity of engine parameters on the lubrication and wear characters were analyzed using the proposed model.Finally,a multi-parameter analysis was conducted to summarize the direction of optimizing the design of main bearing wear in multi-cylinder ICEs for low-viscosity oil applications,and a range of values for the key parameters was given for reference.The main research contents and the key findings obtained were as follows:1.The simulation model of lubrication in the main bearing system of a multi-cylinder ICE for low viscosity oils and its application.A simulation model for the lubrication of the main bearing system of a multi-cylinder ICE was established and solved,taking the viscous pressure effect and shear-thinning effect into account,in view of the increased local total pressure and shear rate of the main bearing for the application of low viscosity oils.A simulation model for the lubrication of the main bearing system of a multi-cylinder ICE for low viscosity oil applications has been improved,and the friction reduction effect of the main bearing system using low viscosity oil has been analyzed,and then the model was applied to a six-cylinder diesel engine under the endurance test conditions.The results showed that the minimum oil film thickness of the main bearing has increased by an average of 2.79% and a maximum of 12.32%;the maximum oil film pressure has increased by an average of 4.7% and a maximum of 25%;the total friction loss has increased by an average of 4.39% and a maximum decrease of 24.2%.The use of low viscosity oils reduced the hydraulic friction loss in the main bearing system by up to 24%,but the increased asperity friction losses offset the total friction reduction effect and there was a certain probability that this would lead to deterioration of the main bearing wear.2.Simulation method of bearing wear for the multi-cylinder ICEs taking the dynamic coupling behavior between the lubrication and wear into account.For the complex main bearing system of a multi-cylinder ICE,a wear simulation model of the main bearing system considering the dynamic coupling of lubrication and wear was established,a wear profile iteration method that balanced the calculation accuracy and efficiency was proposed,a suitable iteration step was given and verified.The results showed that with the optimization of the wear iteration step,the new model reduced the computation time by more than 80%,while the difference in calculation results was less than 3%.3.Research on dynamic coupling mechanism between lubrication and wear of the main bearing system for multi-cylinder ICEs.On the basis of the wear simulation method with dynamic lubrication-wear coupling proposed in this paper,the dynamic wear evolution of the main bearing system was analyzed,and the dynamic lubrication-wear coupling mechanism of the main bearing was revealed.The results showed that the first 60 h of wear of the main bearing system of an internal combustion engine is in the rapid wear phase;the coupling of lubrication and wear during the wear process causes the main bearing mating pair to form a rapid conformal contact.The results showed that the first 60 h of wear progress for the engine was in the rapid wear phase,and the value and position of the wear profile peak of each bearing was mainly influenced by the direction of misalignment of the corresponding main journal.The total pressure at the axial ends of the bearing was greatest at the beginning,and the maximum total pressure was mainly contributed by the asperity contact pressure.The coupling effect between the lubrication and wear during the wear process helped the formation of the conformal contact between the main bearing friction pair.4.Factors and sensitivity analysis of engine parameters on dynamic lubrication and wear of main bearing system.The non-linear factors affecting the lubrication and wear of the main bearing system were analyzed,and a corresponding analysis scheme was designed.The sensitivity of the five categories of factors,namely operating conditions,bearing structure parameters,bearing surface parameters,lubricant parameters,and wear factors,on the dynamic lubrication and wear characteristics of the main bearings was investigated.The results showed that the main factors affecting the load-carrying capacity of the main bearing in order were the rotational speed,the asperity contact ratio,the design clearance ratio,the viscosity of the lubricating oil,and the bearing surface factors;the main factors affecting the friction loss were,in order,the wear coefficient,the rotational speed,the viscosity of the lubricating oil,the design clearance ratio,the surface texture;the main factors affecting the maximum wear depth of the main bearing were,in order,the surface roughness,the length-diameter ratio,the viscosity of the lubricating oil,the rotational speed,the wear coefficient,and the design clearance ratio.5.Determined the range of the key design parameters for the main bearings.Combining the performance of the main bearing in terms of load-carrying capacity,friction loss,and wear characteristics,studies on the selection of the key design parameters for the low viscosity oiloriented multi-cylinder ICEs performance were conducted.The key parameters were the viscosity of the lubricant,the structural factors,and the surface parameters.The results showed that the viscosity of the selected oil should be higher than 9.632 m Pa·s at 100?,the range of the lengthdiameter ratio for the main bearing was in a small range between 0.31 and 0.33,the suitable range for the main bearing clearance ratio was 0.02%-0.03%,the surface roughness of the main bearing needs to be less than 1 micron;the texture direction ratio when processing the longitudinal texture can be limited between 1 and 6.