Research On The Characteristics Of Electro-hydraulic Proportional Axial Variable Piston Pump

The axial variable displacement piston pump is widely applied in the engineering machines and the molding injection machines, on which the research of the low noise and the proportional control technology are the important development trend. At the present, the key technology of the axial variable displacement piston pump is grasped by the foreign companies, the research and manufacture level in our country are on the elementary stage. And, the lagging technology leads to the disadvantages such as poor pressure stability, slow response, high noise, short life and low reliability of piston pumps. Therefore, the research on the key technology of axial variable displacement piston pump has the important social significance, economical significance and engineering significance on improving the competition ability of our hydraulic products. It is proved that the performances of the open-looped and close-looped electro-hydraulic proportional axial variable displacement piston pump are up to even exceed that of the overseas same products by market, which is developed by the SWJTU and Push Driving Co, Ltd in corporation.In this thesis, the way combined into the theory analysis, simulation and experiment is used to research the low noise valve port technology and the stability problems of the pressure and flow control of the piston pumps. The main content is as follows:1. The supporting way of the axial variable displacement piston pump is researched. Based on the dynamic force of the swash plate produced by pistons, the dynamic mathematical models of swash plate supporting are constructed so as to get the key factors which affect the swash plate dynamic performance. By analyzing the swash plate supporting stiffness, it is known that the piston supporting structure has the bigger stiffness than the spring supporting one in the swash plate variable displacement and the improvement of swash plate supporting stiffness is beneficial to improve the dynamic performance and reduce the noise caused by swash plate vibration.2. For the piston pump applied in the molding injection machines, which work in the variable conditions (variable pressure, variable revolution, variable displacement), the low noise valve port plate is researched. Based on considering the oil compressibility, the PumpLinx software, dynamic mesh technology and cavitation model is used to calculated the law about the variable working conditions how to affect the swash plate moment, pressure pulsation, flow pulsation and the volumetric efficiency of valve port. Thereinto, the flow pulsation coefficient is over 25% which is much bigger than the calculated value when the oil compressibility and the valve port structure aren't considered when the variable displacement is applied in the machine, the flow pulsation should be considered and the main factors affecting the valve port volumetric efficiency are presented. And, the effect of the swash plate moment, pressure pulsation and flow pulsation on the noise and variable displacement control of the piston pump. In addition, the effect of the negative overlap angle for the negative overlap symmetry deflexion valve port plate and the piston deflexion angle on the valve port noise is researched and the valve port plate technology which is satisfied with the low noise and variable working conditions.3.The mathematical model of the electro-hydraulic open-looped and close-looped axial variable displacement piston pump is constructed. According to analyze the pressure-flow characteristics of the valve port window, it is found that the simplified formula of the valve port area gradient has certain limitation. The area gradient W(x) can't be calculated directly by multinomial fit formula and the better way is that the multinomial fit is applied after deriving the flow area and the MATLAB programs of the flow area and the area gradient are written. By the comparison research on the pressure-flow characteristics among the rectangle window, circle window, U-type window and V-type window, the principle how to select the adaptive valve port window is confirmed for the compensation valve and proportional flow valve. Furthermore, the main parameters which affect the dynamic performance and the effect disciplinarian are researched, and the match characteristics on the positive open size of compensation valve, the diameter of pressure-drop orifice and the backpressure orifice is researched. Based on analyzing the advantages and disadvantages of the control piston with non-damp and fixed damp, the variable throttling technology of control piston is presented, which has the same advantages of big damp as the fixed damp but discards the disadvantages of the fixed damp with constant flow loss, throttling noise and the easily jamming orifice. In addition, the parameters which affect the stability when the pump unloads are researched in detail so as to present the way that the end angle of control piston is changed to change the flow gain of unloading orifice and conclude the flow area and area gradient formula of the valve port constructed between the orifice and spool slant.4. The experiment research is performed on the electro-hydraulic open-looped and close-looped proportional axial variable displacement piston pumps. By comparison with the simulation, the geometric parameters which affect the dynamic performance of the piston pump and the effect disciplinarian are gotten. Furthermore, the variable throttling technology and the way, which changes the unloading orifice gain of the control piston are verified by experiment. And, the control stability problems of the piston pump appeared in the practical application are analyzed and solved.