Transient Reynolds Equation For Oriented Roughness Based On JFO Boundary Condition And Its Application

Cylinder liner-piston ring is the friction pair with the worst working condition in diesel engine,which reciprocates at unsteady state and high speed under high temperature and pressure,and the lubrication state also changes sharply.In the total friction loss of diesel engine,the friction loss of cylinder liner-piston ring friction pair is a very important part.Thus,reducing the friction loss of cylinder liner-piston ring can improve the efficiency of diesel engine,and reduce fuel consumption and pollutant emissions.What’s more,numerical analysis for lubrication is an important method to study and optimize the lubrication performance of cylinder liner-piston ring.Therefore,it is of great significance for lubrication calculation and optimization of cylinder liner-piston ring friction pairs to establish an average transient flow model of Reynolds roughness including a mass-flow preserving cavitation,which is feasible in terms of calculation quantity and converging.In this paper,the transient homogenization Reynolds equation based on JFO boundary condition for the cylinder-piston ring friction pair is deduced and a transient mixed lubrication model of cylinder-piston ring based on JFO boundary condition is established.Based on above model,the paper research the influence law and mechanism of design parameters of piston ring,lubricant viscosity,surface roughness,texture parameters and arrangement of piston ring surface on cylinder liner-piston ring friction pair of lubrication.The main results are as follows:1.The transient Reynolds equation of roughness orientation based on JFO boundary conditions is obtained by asymptotic homogenization analysis and local roughness orientation assumption.Compared with the flow factor used in average Reynolds equation,the equation can not only consider the effect of surface roughness more accurately,but also consider the conservation of fluid mass in the presence of cavitation using JFO boundary conditions and the calculation results are more realistic.Compared with the homogenized Reynolds equation,the local roughness orientation assumption is introduced into the Reynolds equation,which simplifies the calculation method of equation coefficients from solving partial differential equations to calculating integrals,thereby reducing the amount of calculation greatly.2.Talcing transient Reynolds equation for roughness orientation based on JFO boundary condition as the governing equation of hydrodynamic lubrication,and considering comprehensively about the fluid friction formula,the surface roughness,the lubricant viscosity model,the axial temperature distribution on the inner surface of the cylinder liner and the contact model of the surface micro-convex body,the transient mixed lubrication model of cylinder liner-piston ring is established based on the JFO boundary condition.The model can not only take the loads,temperature and changing relative velocity under complex conditions,surface roughness and the mass-flow preserving cavitation into account,but is also feasible in converging and calculation amount,which provides a powerful tool for lubrication analysis and optimization of cylinder liner-piston ring.The calculated frictional force curve is basically in accordance with the experimental frictional force curve.which verifies the validity of the above model.3.Compared with the average Reynolds equation nodel.the minimum oil film thickness of the lubrication model established in this paper changes more smoothly with the crankshaft angle due to the consideration of fluid mass conservation in the presence of cavitation and the use of non-statistical surface roughness model.In the pressure distribution obtained by the lubrication model established in this paper,the isobars are changed from straight line into curves by the influence of surface roughness.especially in the area with smaller lubrication film thickness,and the maximum oil film pressure is slightly larger than that of the average Reynolds equation model.In the lubrication model established in this paper.the fluid mass conservation in the presence of cavitation is considered.so the area of the cavitation in the diverging region of the piston ring is larger than that of the average Reynolds equation model.4.The simulation results show that for the standard barrel-faced piston ring、when the ratio of the minimum oil film thickness to the texture depth is small,the existence of the texture in the converging region produces a local diverging region and converging region.thereby forming a low-pressure region in the local diverging region.However,a large enough high-pressure region is not generated in the local converging region.which causes the high-pressure region of the converging region of the piston ring to be broken,resulting in a decrease in the bearing capacity of the lubricating oil filn.The existence of the texture in the diverging region produces a local diverging region and converging region,so a low-pressure region and a high-pressure region are formed in the local diverging region,and the cavitation appearing in the low-pressure region limits the pressure value of the low pressure.thereby causing an additional carrying capacity of lubricant oil film.As the ratio of the minimum oil film thickness to the texture depth increases.the breaking effect of the texture in the converging region on the high-pressure region becomes smaller.but the texture increases the average oil film thickness in the convergent region which increases the oil wedge effect,so the texture in the converging zone changes from decreasing the bearing capacity of-the lubricating oil film to increasing the bearing capacity;as the ratio of the minimum oil film thickness to the texture depth increases,the additional bearing capacity becomes smaller,due to the area of the local low-pressure region formed by the texture in the diverging region decreases,but the texture in the diverszing region increases the average oil film thickness in the diverging region which reduces the pressure drop f-rom converging region to the diverging region of the piston ring barrel,therefore,the texture in the diverging region changes from increasing the bearing capacity of the lubricating oil film to the reducing of the bearing capacity.