Research On Variable Displacement Of Asymmetrical Axial Piston Pump

The electro-hydraulic control system can be divided into two categories: valve control and pump control.The valve control system has the advantages of high position control accuracy and fast dynamic response,but its shortcomings such as large throttling loss and low energy efficiency cannot be ignored.Compared with the valve control system,the pump control system controls the direction and speed of the hydraulic cylinder by changing the direction and flow of the pump,eliminating the throttling loss caused by the control valve,and can improve the energy utilization rate of the system to a certain extent.The pump control system has been widely promoted and used.Pump-controlled symmetric cylinder technology is relatively mature compared with pump-controlled asymmetric cylinder,because in the pump-controlled asymmetric cylinder system,auxiliary pumps or auxiliary valves need to be added in the loop.Although it can balance the asymmetry of the flow of the two chambers of the asymmetric hydraulic cylinder,it will bring high cost,loss of energy consumption,complex circuit and other adverse effects.The asymmetrical axial piston pump developed at present basically solves the problem of flow mismatch between the two cavities of the asymmetric cylinder,but there is a lack of research on the variable displacement asymmetrical axial piston pump and its variable displacement stability.In view of the above problems,this paper takes the asymmetric axial piston pump as the research object,proposes the solution of adding orifice structure into the valve-controlled cylinder system,and rederives the mathematical model of the control system through the internal optimization of the inclination control mechanism of the swashplate.On this basis,in order to make the simulation model of the asymmetric axial piston pump more close to the real motion of the pump,combined with UG/ Sim Center 3D and AMESim software,the mechanic-liquid coupling and rigid-flexible coupling models of the asymmetric axial piston pump were built.The correctness of the co-simulation model is verified by experiments.According to the co-simulation model of the asymmetric axial piston pump and the system’s Baud diagram,the influence of the orifice added into the system is studied and analyzed.The research results show that:Adding a 2mm diameter orifice to the control system of the asymmetric axial piston pump has a significant effect.The addition of the orifice can effectively reduce the pressure shock,the variable cylinder piston force,reduce the pulsation frequency of the dynamic response,and reduce the oscillation period of the swash plate inclination angle and the large fluctuation of the variable resistance torque of the swash plate are improved,which improves the stability of the system;And from the open-loop Bode diagram of the system,the phase margin of the system is 87°,the amplitude margin is 32 d B,and the variable displacement asymmetric axial piston pump system is stable;the system bandwidth is about 14 Hz,which can be reduced by reducing the hydraulic pressure.The area of the piston on both sides of the cylinder increases the flow gain of the servo proportional valve,and improves the problem of reduced system dynamic response caused by the orifice.