| Proportional flow valve is a critical component in hydraulic control system.Its output flow can be proportionally and continuously regulated.Cartridge flow valve is widely used in the hydraulic control system because of large flow capacity,good sealing,simple structure,and so on.However,output flow of proportional flow valve is frequently disturbed by the pressure drop.The existing flow valve adopts the pressure drop compensator or cartridge type flow sensor to make the outlet flow constant.Disadvantages of the mentioned methods are low control precision,complex mechanical structure and small flow capacity.In this dissertation,a two-stage poppet proportional flow valve based on the principle of differential pressure digital compensation is proposed.The proposed valve is composed of a Valvistor valve with a flow amplifying function(main stage),high frequency proportional directional valve(pilot stage),a flow compensation controller and pressure sensors.The pressure difference between the main inlet and outlet is fed back to the flow compensation controller by the pressure sensors first,and then the output flow correction control signal is generated by the digital compensator.In order to further improve the performance,the flow observer is constructed to improve the control precision of the proportional flow.The linear relationship among the output flow,the pilot control voltage and the square root of the pressure drop is obtained by establishing the mathematical model of Valvistor valve.Then a digital flow compensation model is established,and a flow compensation controller with bilinear interpolation algorithm as the control strategy is designed.The dynamic and static characteristics of the proposed valve are analyzed by Simulation X software.Simulation and experimental results show that the proposed valve has higher static control precision,and the output flow is not influenced by load variation.The greater the main pressure difference is,the faster the dynamic response of the poppet becomes.As for step change of main pressure difference,the larger the pressure difference is,the weaker the output flow resistance to pressure interference performance is.In addition,the simulation results show that the dynamic and static characteristics of the proposed valve can be improved by the flow observer. |
