| Axial piston pump is the core component of hydraulic system,which is widely used in the servo equipment of aviation,aerospace,and navigation.The multipurpose development of hydraulic technology requires the low speed performance of piston pump to be improved gradually.However,as the most critical friction pair in the axial piston pump,the cylinder block-valve plate pair is extremely dependent on the lubrication of the oil film.The supporting force of the oil film is weak under low speed conditions,and the biased load of the cylinder block leads to serious wear of the friction pair material.The traditional residual compression force method is difficult to meet the lubrication requirements under this condition.Magnetic force has the characteristic of no contact and no lubrication.The compound support of magnetic force and hydraulic pressure can reduce the eccentric load on the cylinder block and make up for the lack of oil film support at low speed,which has important reference value for the design and development of axial piston pump with high reliability and long life.This dissertation firstly introduces the working principle of hydrodynamicmagnetic compound support(HMCS)for cylinder block-valve plate pair in axial piston pump and proposes the magnetic support unit(MSU)as the technical carrier and the key structural components under the condition of ensuring the compactness and reducing the magnetic flux leakage.Based on the virtual displacement method,the theoretical expressions of the magnetic bearing capacity and torque are deduced,and the influence of various structural parameters of the MSU on the magnetic bearing capacity is analyzed.Based on the COMSOL Multiphysics multiphysics simulation software,the finite element simulations of the three-dimensional steadystate magnetic field inside the MSU are carried out,the magnetic bearing capacity of different magnetic pole gaps is calculated,and the internal magnetic field distribution is obtained.The important factors affecting the magnetic bearing capacity are put forward through comparative analysis.Then,the dynamic model of the magnetic cylinder block is established.The trajectory of the action point of the pressing force,the difference of the moment radius,and the tilt torque of the cylinder block are calculated under the low speed condition.The influence of the MSU on the balance of the cylinder block is comprehensively analyzed.Comparing the magnetic bearing capacity calculated by theory and simulation models,considering that the end effect of the axial stator has a great influence on the magnetic bearing capacity,flux tube models at the end of the axial stator are established based on the simulation of the internal magnetic field,and the correction of the magnetic bearing capacity model is completed,the principle prototype of the MSU is processed,and the experimental method for the bearing capacity of the MSU separated from the pump body is proposed.The magnetic bearing capacity test rig is designed and built,the magnetic bearing capacity under different magnetic pole gaps is measured,and the correctness of the theoretical and simulation results is verified.In order to explore the influence of temperature on the performance of the MSU,a temperature prediction model of the MSU is established based on the control volume method,and the influence of various working conditions on the transient temperature of the MSU is obtained.The test rig of MSU temperature characteristics is designed and built,and oil flows of different temperatures and flow rates are introduced into the MSU.The magnetic bearing capacity of the corresponding working conditions is measured.The temperature distribution of the MSU is obtained by thermal imaging,which verifies the correctness of the theoretical model.On the basis of in-depth analysis of the dynamic characteristics of the magnetic cylinder block,the coupling relationship is established between the magnetic field,oil film pressure field,and the structural field related to the cylinder block-valve plate pair based on HMCS.A mathematical description of the oil film geometry is carried out considering the tilt of the magnetic cylinder block and the elastic deformation of the material surface.In order to improve the data transfer efficiency between the oil film pressure field and the structure field,the influence matrix of the elastic deformation of the magnetic cylinder block and the valve plate is calculated by the influence coefficient method,and the obtained deformation is superimposed on the solution results of the Reynolds equation.Considering the inherent pressure pulsation of the piston pump,the dynamic pressure boundary condition is established,the numerical model of oil film lubrication based on HMCS is proposed,the model solving process is given,and the change of the oil film structure under different pressure and speed is analyzed.The lubricating characteristics of the oil film before and after adding the MSU are analyzed comprehensively.Finally,combined with the structural configuration of the magnetic cylinder block and the MSU,a test rig for lubrication characteristics of cylinder block-valve plate pair based on HMCS is designed and built.The eddy current sensors are used to measure the micro-displacement of the end face of the magnetic cylinder block under different pressures and rotational speeds.Then the variation law of the oil film thickness at each measuring point is analyzed,and the influence of the MSU on the dynamic pressure effect of the oil film is obtained.The minimum micro displacement at the same position before and after adding the MSU,the angle of occurrence,the average micro displacement,and the slope of the cylinder block inclination angle are compared and analyzed.When adding MSU,the minimum oil film thickness increases by 17μm,35μm,31μm and 29μm respectively when the pressure is 2MPa and the rotation speed is 200r/min,400r/min,600r/min and 800r/min.The average oil film thickness increases by 12μm,14μm,9μm and 5μm,respectively.The inclination angle of cylinder block is reduced by 38%,60%,44% and 56%respectively.When the pressure is 7MPa,the minimum oil film thickness increases by 8μm,29μm,40μm and 34μm at the rotational speed of 200 r/min,400 r/min,600r/min and 800r/min,respectively.The average oil film thickness increases by 5μm,10μm,11μm and 7μm,respectively.When the rotation speed is is in the range of400 r /min ～ 800 r/min,the inclination angle of cylinder block decreases by 64%,78%and 76%,respectively.The experimental results are basically consistent with the changes of the oil film structure obtained by the simulation,which verifies the correctness of the numerical lubrication model of the cylinder block-valve plate pair based on HMCS,laying a foundation for theoretical development and technical application of HMCS for cylinder block-valve plate pair in axial piston pump. |
