Research Of Transient Thermo-hydrodynamic Lubrication Of Surface Textured Cylinder Liner-Piston Ring Assemblies

The lubricant film between the contact surfaces of the piston ring-cylinder liner,one of the most important frictional components in an internal combustion engine,is influenced in the actual operating environment not only by the combustion gases and the heat transferred from the cylinder liner walls,but also by its own internal shear forces and the heat transferred from the piston ring to the lubricant.Temperature changes in transient thermal fluids can have an effect on the viscosity of the lubricant,which in turn affects the lubrication characteristics of the friction pair.The friction losses generated by the piston ring-cylinder liner friction pair account for approximately 40%of the friction losses in piston-ring-cylinder liner assemblies.To reduce friction losses and improve lubrication performance,surface weave technology is widely used.This thesis couples transient thermo-hydrodynamic lubrication with surface weaving technology to analyse the effect of surface weaving technology on the lubrication characteristics of piston ring-cylinder liner assemblies under a transient thermo-hydrodynamic model.First of all,based on the mean Reynolds equation and the Greenwood-Tripp micro-convex contact model for non-smooth surfaces,a numerical model of the transient thermal fluid lubrication characteristics of the piston ring-cylinder liner assembly is established by combining the oil film thickness equation,the energy equation,the viscous temperature and viscous pressure characteristics of the lubricant,which can truly reflect the tribological behaviour characteristics of the piston ring-cylinder liner assembly of an engine throughout the working cycle.The model can be solved to obtain accurate numerical solutions for the pressure,temperature and thickness of the lubricant film between the friction surfaces of the piston ringcylinder liner assembly.This gives a more accurate representation of the effect of temperature changes in the film on the lubrication characteristics of the piston ring-cylinder liner assembly during operation.And then,by comparing the results of the calculation of transient thermal fluid and isothermal thermal fluid for the textured piston ring-cylinder liner assembly,it is concluded that the change in lubricant temperature during the operation of an engine is not negligible and that the results are more realistic considering the transient thermal fluid model is more responsive to the actual operating process.The radius,surface density and depth of the micro-pits have a greater influence on the lubrication characteristics.Finally,the lamellar liner-piston ring test specimens were machined to verify the accuracy of the numerical calculation model through UMT reciprocating friction and wear tests.18 surface weaving solutions were designed based on the previous simulation analysis,and the best weaving solution was selected through UMT friction and wear tests.From the measured results,it can be seen that the crater depth in the liner weave has a greater effect on friction reduction,followed by the crater radius.The ability of the liner surface weave to reduce engine back drag torque and improve fuel economy is corroborated by the UMT tests and simulations,demonstrating the positive effect of surface weave on friction reduction.