Lubrication Characteristics And Parameter Optimization Of Plane Barrel-Port Plate In Axial Piston Pump

Hydraulic axial piston pump has been commonly used in the majority of fluid power applications for specific advantages such as compact dimension,high power density and long lifecycle.However,excessive wear and internal leakage have adverse effects on the volumetric efficiency and life expectation of piston pump,which are mostly determined by the operating condition of three critical tribo-pairs inside this type of pump,especially the characteristics of lubricating oil film within each moving tribo-pair.As its great importance and complicated mechanism,the oil film in axial piston pump has been a frontier research topic in the field of fluid power transmission and control.Therefore,the oil film characteristics within the barrel-port plate,one of three critical tribo-pairs,were investigated in this thesis, which could be used as a specific theoretical reference to design a new generation of axial piston pump.According to simulation and experimental results of the oil film formation,an algorithm was developed for the film configuration of the sealing regions on the port plate.In this algorithm, a set of experimental values of film thickness replaced the corresponding node point values in numerical method for solving the fluid film equations.Calculated results from this algorithm can be used in predicting the distribution of the wedge film within the pair.In order to calculate accurate barrel-port plate leakage rate,a new mathematical model using the wedge oil film was developed.In this model,barrel tilting and port plate structure are considered in the gap laminar flow.When the wedge oil film is evaluated,the relationship between the film shape and the leakage is established.It was shown in the comparison of calculated and measured results under different structure and operating conditions that the barrel-port plate leakage rate was accounted for about 35%of the total leakage with 20μm of film thickness, which basically meets the requirements of leakage distribution among three critical tribo-pairs. When the film thickness was maintained within 5～15μm,it may be used as an optimal range for the barrel-port plate gap.Simulation results of steady state and dynamic leakage were found reasonable agreements with experimental results,in which the leakage model developed in this thesis is validated to describe the characteristics of the barrel-port plate leakage.Thus,the leakage calculation can be used as a reference in determining the optimal distribution ratio of internal leakage for this type of pump.In addition,one parameter constraint of the lubricating oil film has been implemented in the geometry optimization for the barrel-port plate,which becomes an important part of piston pump optimization.Compared with the previous optimal study when lubricating oil film was not considered,the calculated results in the thesis can meet the necessary running conditions of barrel and port plate.Moreover,theoretical calculation of the tribo-pair can reduce leakage rate and increase stiffness lubrication film within this tribo-pair, which is helpful to improve the volumetric efficiency and lifecycle of axial piston pump.In Chapter 1,advantages and present technical difficulties of axial piston pump were introduced,functions and breakdown patterns of barrel and port plate were outlined,also the purpose and significance of the study on lubricating oil film within the pair were analyzed.In Chapter 2,the hydraulic control system of the test rig for the barrel-port plate was modeled using AMESim,and the dynamic properties of the gap between barrel and port plate were simulated.Film thickness between barrel and port plate was measured and an algorithm was developed for the lubrication film configuration.In the algorithm,experimental values of film thickness were used to solve the oil film equation and the wedge film distribution between the gap of barrel and port plate was predicted using simulation.In Chapter 3,based on the Reynolds equation for disk gap-flow,pressure formula for the sealing region on the port plate was derived.The applicable linearization condition of pressure distribution was obtained according to the calculation accuracy.The fields of pressure,speed and temperature are numerically analyzed using CFD software.In Chapter 4,a mathematical model was developed to calculate the barrel-port plate leakage rate using the wedge oil film.In this model,the barrel tilting and the port plate structure were considered,and the corresponding relationship between the wedge film and the leakage rate was established.Simulation of the barrel-port plate leakage rate under different operation conditions was verified by experiments,and the distribution ratio in the total leakage of piton pump was obtained.In Chapter 5,studies on friction torque between the barrel and port plate and its effects on mechanical efficiency of piston pump were carried out.Friction torque was measured under different operating conditions and its mechanism combined with the rotational cycle of barrel was discussed.Besides,bearing force between the barrel and port plate versus supply pressure was tested under different film thickness and rotation speed.In Chapter 6,the sealing region of port plate was optimized,in which the lubrication parameter was implemented as a new constraint condition.It was shown in the calculated results that the leakage rate reduced while the stiffness of oil film increased,which can provide a specific reference for optimization of tribo-pairs in piston pump.In Chapter 7,conclusions were summarized and the future research developments were proposed in this chapter.