| The ball piston pump is a kind of radial hydraulic pumps with balls as pistons. It isavailable for higher pressure and higher speed and be fit for used in HMT. With theincreasing requirement for high speed and heavy load, the ball piston pump is an incrediblypromising pump form. The accurate working mechanism and the characteristics of keycomponents in the pump is unclear, and the designing theory is not mature. Therefore, theauthor aims to build up a tribo-dynamic model of the ball piston-ring-cylinder assemblythat covering the coupled influences of kinematics, elastohydrodynamic lubrication (EHL)characteristics, and dynamic behaviors. In the present study, a dynamic contact model ofball piston pump with the contact stiffness and damping characteristics in consideration isestablished. A prototype was designed and tested.First according to the analysis on motion and static forces, a hypothetic model of ballpiston components is built. The primary stress distribution and movement rule of contactpairs at every positions and time are getting from the model. The ball-cylinder pairs are inthe state of point contact EHL with varying load, varying entrainment velocity, and largeslip ratio. The boundary slip effect is taken in the model and the slip velocity is analyzed.Rheological model of Circular and the limited shearing stress theory is used in thecalculation of equivalent viscosity which is led into Reynolds equation. The multilevelintegration method is introduced to speed up the calculation of surface simultaneously.Besides, the Gauss-Seidel iteration and multilevel method are used to obtain the lubricatingcharacteristics. Accordingly, the influence of coefficient of friction of this pair in differentworking condition is revealed. Test results verified the accuracy of the tribologicalsub-model.For dynamic modeling, coordinate systems and the transform relationship areexplained at first. The forces, moments, velocity and acceleration on ball-cylinder pair,ball-ring pair and cylinder-distribution shaft pair are analyzed completely. The deformationand the viscosity resistance are including in the model. Dynamic equations are solved using numerical approach method. The structure deformation on all these components which isco-simulation using FEM and EHL method has serious implications for the lubricationcharacteristics. Based on the dynamic model structure and the tribological sub model, atribo-dynamic model with multi-factors nonlinear coupling is established.Through the tribo-dynamic model, dynamic characteristics of ball pistons are gainedunder different working conditions and structures. The revolution speed and spin speed areanalyzed to show out the state of slip between ball and ring. Contact and friction forceswith lubrication model which vary by time are descriptioned accuratly. Some specialstructures like hollow ball, copper cover and larger ring are considered to changed dynamiccharacteristics, and several suggestions for design are listed. The leakage model ofball-cylinder pair is built and the volumetric efficiency can be simulated. A prototype pumpwith displacement of300cm3/r and a test device for leakage is designed and the test benchsystem is built for the confirmatory testing. Results of testing fit the simulation results well. |
