Study On Surface Topography And Simulations To Predict The Cylinder Block/Valve Plate Interface Performance In Axial Piston Machines

Swashplate axial piston pump is widely used in aviation,aerospace,ship industry,and engineering machinery.Because of their ability to operate at high pressures and speeds while maintaining high efficiency.The cylinder block/valve plate friction pair is the most critical friction pair component.Excellent mechanical performances,wear resistance,and sealing performance are guaranteed for its serving with long life in extreme working conditions.However,when the pump operates at low speed,poor interface lubrication can aggravate the worn-out cylinder block/valve plate friction pair,even reducing the lifetime of the pump body.The oil film on the interface of the cylinder block/valve plate friction pair does not only needs to bear the external load but also plays a lubrication role in the interface,which can maintain the lubrication characteristics of the cylinder block/valve plate friction pair and ensure the high-efficiency operation of the pump.The inability of the oil film to keep the external load at high pressure and poor surface treatment for the dissipation of frictional heat causes the interface to wear.To solve the above problems,previous researchers have developed the surface wear-resistant coating to improve the wear resistance of the cylinder block/valve plate friction pair.However,texture on the wear-resistant coating introduces surface rumpling,which can destroy the original structure of the friction pair surface and increase the local deformation of the surface.It has a negative impact on the friction pair’s wear resistance.Given this problem,this project first analyzes the dynamic characteristics of the cylinder block/valve plate friction pair through theoretical modeling and numerical simulation to explore the influence of the surface roughness parameter on its leakage flow and the main reasons for the volumetric efficiency loss are revealed.Which provides theoretical guidance for optimizing the interface structure of the cylinder block/valve plate friction pair.Secondly,Cubased wear-resistant coatings with different microstructures were designed and prepared to verify the above simulation theory.The specific research contents are as follows:(1)To optimize the interface design of valve pair and improve its wear resistance,a numerical model was established to predict the micro dimple radius on the valve plate and better understand its interface wear and elastic deformation mechanism.The influence of temperature on oil kinematic viscosity and surface deformation with different working conditions were also studied.The solid-body dynamic and material tribological behavior on loading force and thermal effect has been well analyzed using three different materials of the valve plate,namely,bronze coating with38 Cr Mo Al substrate(P1),PVD-bronze coating with 38 Cr Mo Al substrate(P2),and nitrided bulk ductile iron(P3).The results show that increasing the surface roughness value influences the leakage flow and the pressure build-up on the friction interface.Lead bronze PVD coating of the valve plate shows better tribological performance due to the optimal correlation between materials microstructure,desired toughness,and hardness,which possibly possessed wear resistance(2)To verify the simulation results,the same mechanical properties of the three different coating materials were designed and prepared on a 38 Cr Mo Al matrix,such as bronze coating38 Cr Mo Al matrix(P1),PVD coating 38 Cr Mo Al matrix(P2),and nitrided nodular cast iron38 Cr Mo Al matrix(P3).The wear resistance of the above coatings under different loading forces was investigated using oil environment friction and wear test.The effects of the different coatings composition and microstructure on the wear resistance of the coatings were analyzed.The results show that the surface roughness of the interface influences the coefficient of friction and the wear rate of the valve plate materials.Therefore,an appropriate Ra value of ～ 0.4 μm is required to obtain optimal tribological interface performance when the valve plate surface is being textured.Also,the lead bronze PVD coating(P2)of the valve plate exhibited excellent tribological performance.Its appropriate phase composition and microstructures were believed to be responsible for better tribological performance,which agrees with the simulation results.Combined with the characterization of coating hardness,the failure mechanisms of the coatings are revealed.This project can provide guidance for the optimal design of the cylinder block/valve plate friction pair in the swashplate axial piston machine.