| Swashplate-type axial piston pump has been widely applied in robotics,aerospace,shipping,and other industry fields ascribed to their high operating pressure,variable displacement,high power density,and high efficiency.The three friction pairs,including cylinder block/valve plate,piston/cylinder block,slipper/swashplate,are the important lubricating interfaces in swashplate-type axial piston pumps.The unbalanced pressure distribution on the valve plate will result in the breakdown of the oil film and abrasion wear between the valve plate and cylinder block.Surface micro-textures,as a surface modification method,have been proved to ameliorate the tribological behavior of frictional pairs effectively.Therefore,it is revealed that the influence of surface microtextures on the friction and lubrication performance of the cylinder block/valve plate can be monitored to reduce its viscous friction and wear,thereby reducing power loss,and improving its efficiency.Firstly,based on the hydrodynamic lubrication,the cylindrical,spherical,rectangular,elliptical,chevron micro-textured valve plate/cylinder block lubrication model was established.The finite difference method was employed to solve the discretized Reynolds equation to obtain the pressure distribution.Further,the oil film pressure distribution and load-carrying capacity of the chevron micro-textured surface with rectangular and circular cross-sectional profiles are analyzed to obtain the optimal cross-sectional shape.Studies have shown that the average oil film pressure and load-carrying capacity of the chevron micro-texture are the highest among the cylindrical,spherical,rectangular,elliptical,chevron micro-textures.The average oil film pressure and load-carrying capacity on the chevron micro-textured surface with a circular cross-section profile were higher than those of the chevron micro-textured surface with a rectangular cross-section shape.Secondly,the chevron micro-textures with different depths were manufactured by micro-milling on the valve plate.The friction coefficient,wear topography,wear mechanism,and XPS analysis of chevron micro-textured surface were analyzed after the disk-on-disk tribological tests.The results showed that as the depth of the chevron microtexture increased,the friction coefficient of the chevron micro-textured valve plate firstly decreased and then increased.Compared with the untextured valve plate,the chevron micro-textures with depths of 10 ?m,20 ?m,30 and 40 ?m can reduce the friction coefficient and wear scars depth.The wear mechanism was not changed by chevron micro-textures.Both abrasive and adhesive wear were observed on the untextured and chevron micro-textured surfaces.However,compared with the untextured surface,only slight abrasive and adhesive wear were observed on the chevron micro-textured valve plate.Then,based on micro-milling and wet micro-blasting,the multi-scale micro-textured surface was manufactured on H62 brass.The wet micro-blasting was applied in the H62 brass after the surface micro-texturing.The surface topography of multi-scale microtextured samples processed by three abrasive grit sizes accompanied by two processing times was comprehensively measured in terms of height,spatial,hybrid,feature,functional,and functional volume parameters.The tribological performance of multiscale micro-textured H62 brass was characterized by disk-on-disk frictional experiments.Through analyzing the relationship between surface morphology and tribological properties,the anti-friction mechanism of the multi-scale micro-textured surface was analyzed from the perspective of 3D surface roughness parameters.The friction coefficient and wear mark depths of the multi-scale micro-textured surface processed by the combination of micro-milling and wet micro-blasting decreased with the increasing grit size and micro-blasting time.Finally,to accurately obtain the pressure distribution between the micro-textured valve plate and the cylinder block friction pair,the cavitation based on the actual working conditions was considered in the present lubrication model.Firstly,the entire cylinder block/valve plate interface was simulated using the simulation tool Multics considering the dynamic loading,the squeeze motion,the analytical pressure deformation,mixed friction,and cavitation.A Matlab scripture was used to analyze the simulation results from the first step and identify the critical low film thickness area that has the risk for abrasion wear.Secondly,the simulation tool Multics was used again to simulate the fluid behavior using the high-resolution distributive boundary conditions from the second step in the small,refined area.The small region high-resolution simulation was capable of simulating the lubrication performance with different types of micro-textures and assessing their effects on the load-carrying capacity.Finally,the effects of chevron microtexture depth,width,distance on the lubrication performance of micro-textured valve plate/cylinder block were investigated by the Multics simulation.The research results showed that whether cavitation occurred inside the micro-texture was affected by the depth of the chevron micro-texture.The best lubrication performance could be observed when the depth of the chevron micro-texture was close to the oil film thickness between the valve plate and the cylinder block.The width of the chevron micro-texture affected the area of the cavitation region.As the width of the chevron micro-texture increased,the load-carrying capacity of the oil film between the chevron micro-textured valve plate and the cylinder block became higher.The chevron micro-texture distance presented an influence on the size of the convergence zone where the positive pressure generated.Small micro-texture distance was not conducive to the generation of positive pressure in the convergence zone.Large chevron micro-texture distance led to a decrease in the number of micro-textures,which was also not conducive to enhancing the lubrication performance between the valve plate and the cylinder block. |
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