| Energy saving and high efficiency are the research emphasis and difficulties of hydraulic transmission technology.Compared with the valve control system,the variable-displacement pump control system can significantly improve the energy utilization efficiency,reduce the system installed power and heat,as well as improve the reliability and service life,bringing considerable economic benefits for the end users of the host equipment.Therefore,pump control system to replace the valve control system is the future development trend of hydraulic transmission technology.As the research object of this dissertation,the axial piston pump is the power source of the pump control system.The efficiency performance of axial piston pump in its full operating ranges has become increasingly prominent in the efficiency performance of the overall pump control system.Therefore,based on this background and motivation,this thesis focuses on the investigation of the variation and distribution characteristics of the efficiency as well as the power losses of axial piston pump,and study on the mechanism of energy dissipation as well as the tribology design technology for the surface topography of friction pairs of axial piston pump.Firstly,based upon the combination method of mathematical theory analysis,dynamic simulation modeling and experimentally test,the variation and distribution characteristics as well as the mechanism of friction losses and volumetric losses of axial piston pump,are investigated under different pressure,speed and displacement conditions.The overall efficiency of axial piston pump is discovered which decreases fast with the decrease of pump displacement.Axial piston pump works in the low efficiency area as well under the condition of low pressure.In the low efficiency area,the decrease of the overall efficiency of axial piston pump is in the range of 68-97%due to the friction losses of the friction pairs of pump.Therein,the friction losses in piston/cylinder pairs and slipper/swash-plate pairs were discovered being the main sources of power losses of axial piston pump.Furtherly the film-forming mechanism and lubrication bearing mechanism of oil film in the clearance of friction pair have been analyzed.The piston/cylinder pair was chosen as the research object,due to the piston/cylinder pair representing one of the most critical design elements as well as the uppermost energy dissipation source of axial piston pump.The complex fluid-structure interaction phenomena in the interface of friction pair and its solution method have been studied in this thesis.The hydrodynamic lubrication model and the elastohydrodynamic lubrication model of piston/cylinder pair have been developed,considering the squeeze film effect and the change of oil film thickness due to the solid boundaries elastic deformations caused by the oil film pressure.In order to experimentally study the performance of piston/cylinder pair,a test rig was built to synchronously measure the axial friction force and lateral force of piston/cylinder pair.The available testing conditions of test rig can reach a large displacement,high speed and high pressure condition,in order to meet the test requirements of the high-speed development trend of axial piston pump.By comparing with the measurement results based upon the test rig,the developed mathematical model of the dynamics of piston/cylinder pair,and the developed lubrication model of piston/cylinder pair,as well as the developed simulation model of the dynamics of test rig were verified.The friction force of piston/cylinder pair under the different speed and pressure conditions were measured and analyzed.For the purpose to improve the lubrication performance and load carrying capacity.and reduce the friction force of piston/cylinder pair,the tribology design method for the surface topography of piston/cylinder pair has been proposed and developed.The impact of the different structures of surface topography of piston bores on the energy dissipation of piston/cylinder pairs have been investigated theoretically and experimentally,respectively based upon the proposed tribology design method for the surface topography of piston/cylinder pair,and the test rig of piston/cylinder pair.The piston/cylinder pairs formed with a proposed innovative conical piston bore,have been discovered which have lower volumetric losses,lower friction force and higher lubrication bearing capacity under the different operating conditions,compared with the conventional cylindrical piston bore.The proposed innovative conical piston bore has a relatively good processibility as well.The proposed innovative conical piston bore,which has a height difference of conical zone being 46.67%of the height of the clearance in cylindrical zone,and a distribution length of conical zone being 49.44%of the maximum contact length between piston and piston bore,has been recommended as the comprehensive optimal surface topography structure of piston bore.The thesis is outlined as follows:In chapter 1,the state of the art in the world relevant to the energy dissipation analysis,and the tribology design technology for the surface topography of friction pairs of axial piston machines,as well as the test technology for the forces of piston/cylinder pair,has been investigated and reviewed.The main research subjects and contents in the thesis werediscussed.In chapter 2,the variation and distribution characteristics of efficiency and various power losses,including the various volumetric losses and friction losses of axial piston pump in the full operating range,were analyzed theoretically and experimentally.In chapter 3,the film-forming mechanism and lubrication bearing mechanism of oil film in the clearance of friction pair were analyzed.The complex fluid-structure interaction phenomena in the interface of friction pair and its solution method were studied.The lubrication model of piston/cylinder pair have been developed,considering the squeeze film effect and the change of oil film thickness due to the solid boundaries elastic deformations caused by the oil film pressure.In chapter 4,a test rig was built to synchronously measure the axial friction force and lateral force of piston/cylinder pair.The available testing conditions of test rig can reach a large displacement,high speed and high pressure condition.The developed mathematical model of the dynamics of piston/cylinder pair,and the developed lubrication model of piston/cylinder pair,as well as the simulation model of the dynamics of test rig were verified experimentally.The friction force of piston/cylinder pair under the different speed and pressure conditions were measured and analyzed.In chapter 5,the tribology design method for the surface topography of piston/cylinder pair has been proposed and developed.The impact of the different structures of surface topography of piston bores on the energy dissipation of piston/cylinder pairs have been investigated theoretically and experimentally.The piston/cylinder pairs formed with a proposed innovative conical piston bore,have been discovered which have lower volumetric losses,lower friction force and higher lubrication bearing capacity under the different operating conditions,compared with the conventional cylindrical piston bore.The proposed innovative conical piston bore has a relatively good processibility as well.In chapter 6,the research contents and the maim conclusions were summarized.Some future works were suggested. |
PDF Full Text Request