Research On Oil Film Characteristics Of Slipper Pair In Axial Piston Pump

As a core power component in hydraulic transmission systems,axial piston pumps are widely used in the field of heavy machinery and defense equipment because of their advantages such as compact structure,high power density and available flow regulation.The axial piston pump performance determines the reliability and life of hydraulic system.The continued development of fluid power system has put forward higher demand upon axial piston pumps for greater delivery pressures and rotational speeds in order to achieve higher power density.However,high rotational speed brings new challenges to the pump design,especially to the slipper/swash plate interface design.Under normal operating conditions,the slipper is subjected to tilting moments due to centrifugal force,ball joint friction,and viscous friction under the slipper sealing land.These tilting moments significantly affect the lubrication characteristics of the slipper/swash plate interface.Specifically,a potential metal-to-metal contact between the slipper and the swash plate is likely to occur due to these tilting moments,which reduces the reliability and service life of the pump.Therefore,a proper design for the slipper/swash plate interface is needed to avoid detrimental slipper wear.However,the complicated kinematics makes slipper/swash plate interface design a difficult issue.To better understand the slipper’s lubrication performance,this thesis mainly focuses on the development of numerical model,the special test rig,and the novel retaining mechanism.A numerical model has been built and its accuracy has been improved by considering the effects of the slipper spinning speed and centrifugal force of oil on the slipper lubrication characteristics.The thesis is outlined as follows:In chapter 1,the background of the subject is briefly introduced.The research on the lubricating oil film between the slipper and swash plate at home and abroad was divided into two categories:numerical model and test rig.And the main research contents in the thesis were discussed.In chapter 2,a numerical model for lubricating oil film of the slipper/swash plate interface was built.In order to improve the accuracy of the numerical model,the mechanism of the slipper spin was examined.Then,the kinematic and dynamic characteristics of the piston/slipper assembly were analyzed in detail.The slipper spinning speed and the centrifugal force of oil were taken into consideration when establishing the pressure equation for the slipper bearing.In chapter 3,the characteristics of the slipper spin and the oil film were analyzed.The importance of considering the slipper spin in the numerical model was verified by comparative analysis for the oil film characteristics under two extreme cases:slipper spinning speed is equal to pump rotational speed or zero.By means of simulation and experiment,the friction coefficients of ball joint and piston/cylinder friction pair were determined by comparing simulation results of the piston spin speed and friction force of piston/cylinder friction pair with the test results.The slipper spinning speed was calculated by the oil film simulation model,and the effect of operating conditions on the slipper spin speed was analyzed.The characteristics of oil film were given under different conditions.In chapter 4,the test method of oil film distributed parameters and slipper spin speed were presented,and the test platform was established.The slipper spinning speed was measured indirectly via a followed sensor fixed on the retainer.To solve the contradiction between the continuous measurement of oil film pressure/thickness field and the limited space as well as cost,a variable angle shaft transmission mechanism was proposed to obtain the changing microscopic characteristics of oil film over one cycle.Based on the proposed test method,the predicted results of slipper oil film model accorded well with the measured data under different conditions.This test platform could be used to verify the oil film model of slipper and optimize the design of slipper structure.In chapter 5,a novel partitioned retaining mechanism with fixed clearance was put forward.The key points of designing and main functions of the retaining mechanism were introduced,and the oil film model of the retainer/swash plate pair was established.The oil film characteristics and energy dissipation were presented under different conditions.The macro output characteristics of axial piston pump with different retaining mechanism were compared with each other in detail,and the experimental results showed that the axial piston pump with partitioned retaining mechanism with fixed clearance improve the reliability with sacrificing efficiency.In chapter 6,the research contents and the conclusions were summarized and some future work was suggested.