Research On Water Hydraulic Internal Gear Pump With Involuted Gears

At present, piston pumps are the most common structure forms in water hydraulic pumps. Although performances of some water hydraulic piston pumps have reached or even over those of oil hydraulic ones, they still have shortcomings which are caused by their structure forms, such like complicated structures, sensitive to contaminants, bad suction performance, large flowrate and pressure pulsation, high level of vibration and noise and so on. To a certain extent, these shortcomings have restricted the application and development of water hydraulic technologies. Water hydraulic internal gear pumps have combined the advantages of green water hydraulic technologies and high-pressure internal gear pump technologies, which makes they overcome the shortcomings of traditional water hydraulic pumps and consistent with the development trend of hydraulic pumps, such as higher operation pressure, higher operation speed, more compact and more greener.In this dissertation, a new kind of involute internal gear pairs, short for "involute internal gear pairs" are chosen as the key components of water hydraulic internal gear pumps. Compared to the conventional involute gear pairs, these new gear pairs can decrease the useless dead volumes and trapped volumes, which can improve the performances of internal gear pumps. Firstly, a parametric mathematical modeling method of conjugated involute internal gear pairs is proposed and then the graphical modeling method is presented. With the mathematical models, meshing characteristics of the gear pairs are discussed and the limiting conditions to avoid overcutting are derived. Then, the parametric instantaneous flow equation of the internal gear pumps is obtained. And, some indexes are proposed to evaluate the influences of gear parameters on fluid transport performance. Also, the influences of meshing characteristics on trapped volumes are discussed and a graphical method is presented to investigate influences of gear parameters on trapped oil characteristics, based on which the structure for eliminating trapped oil is designed. With the help of graphical model of gear pairs, the unbalance radial forces acting on internal gear pairs can be accurately solved, which are periodically changing with gear rotation. According to the unbalance radial forces, the hydrostatic bearing forms are determined for the two key friction pairs, which are gear shaft-sliding bearing and internal gear-pump case, under water lubrication conditions. Components are designed to compensate gaps and make axial and radial gaps always at a lower level. With the help of FEA tool, results of stress and deformation of these components during the operation process are obtained. And, the deformation-resulting leakages are analyzed. The main technical specifications of water hydraulic internal gear pumps are determined, which help to determine the parameters of internal gear pairs. Based on the operation conditions, materials for key components are chosen and so are the machining methods. Finally, referring to the standards of oil gear pumps, an experiment system for water hydraulic internal gear pumps is designed, which lays the foundation for the experiment researches and the following optimization and improvement of the pumps.In Chapter1, the development status and shortcoming of existing water hydraulic pumps are briefly described. The source, purpose and significance of this dissertation are introduced. With descriptions of development statuses of modern water hydraulic technologies and internal gear pump technologies, the advantages of water hydraulic internal gear pumps are pointed out. The key problems and main research contents are listed.In Chapter2, the mathematical models of involute internal gear pairs are built based on double generating method. With the obtained mathematical models, the graphical models of the gear pairs are built. Then, the meshing characteristics of internal gear pairs are analyzed. Moreover, the limiting conditions to avoid overcutting are derived according to the gear meshing principles.In Chapter3, the parametric instantaneous flowrate formula of involute internal gear pairs is derived. Three indexes are proposed to evaluate the fluid transport performances. And, the influences of module, shifting coefficient, tooth number, pressure angle and fillet radius are discussed.In Chapter4, the influence of meshing characteristics on trapped oil is discussed. A solving method for trapped oil characteristics is presented, which is based on the graphical models of internal gear pairs. Then, the influences of module, shifting coefficient, tooth number, pressure angle and fillet radius are discussed. With the obtained trapped oil characteristics, structures for eliminating trapped oil are designed. In Chapter5, based on the graphical models, a method for solving unbalance radical forces, which are acting on the internal gear pairs, are proposed. And then, the unbalance radical forces are obtained, which are periodically changing with gear rotation. With these results, the hydrostatic bearing forms are determined for the two key friction pairs, which are gear shaft-sliding bearing and internal gear-pump case, under water lubrication conditions. Also, the influences of hydrostatic bearing parameters on bearing capacity and leakage are discussed, which helps to optimize the hydrostatic bearing parameters with larger bearing capacity and smaller leakage.In Chapter6, the operation principles of compensating axial and radial gaps are presented, which are achieved by using floating plates and crescent plates. According to the characteristics of reverse pushing forces, the back-pressure chamber of floating plates is designed. With the help of FEA tools, the results of stress and deformation of floating plates and crescent plates are obtained, which help to calculate the leakage occurring during the gap-compensating process.In Chapter7, the main technical specifications of water hydraulic internal gear pumps are determined and so are the design parameters of internal gear pairs. Then, the machining methods with higher accuracy are chosen for the internal gear pairs and so are the machining methods for floating plates, crescent plates and sliding bearings, whose material is composite plastic. Finally, an experiment system for water hydraulic internal gear pumps is built and based on experiments analyses on operation performances and failure modes are carried on.In Chapter8, conclusions of this dissertation are made and so are some outlooks for the further research of water hydraulic internal gear pumps.