Research On Characteristics And Control Method Of Load Sensing System Based On Independent Inlet And Outlet

Valve control system has the characteristics of good dynamic performance and high control accuracy,so it is widely used in the industrial field.However,since the pump source always outputs constant flow and pressure,the design system needs to design the oil source according to the maximum load condition.Therefore,under the condition of lower load,the output power of the pump source is far greater than the actual power of the load,resulting in large throttling loss and overflow loss.In addition,the throttle area of the inlet and outlet is related to the displacement of the spool.There is a problem of the linkage throttle of the inlet and outlet,which will also increase the energy consumption of the system.Aiming at the problem of low energy efficiency of valve control system,this paper combines the load sensing technology and independent metering technology to solve the problem of pump source and load mismatch and the coupled throttling between the oil inlet and oil outlet in the valve control system.Firstly,taking the load sensing technology as the starting point,the working principle of the electro-hydraulic load sensing system based on speed regulation is analyzed,the mathematical model of the system is established,and the control method of pressure feedback and flow feedforward is used to regulate the output pressure of the pump source.The pressure characteristics and energy efficiency of load sensitive system and valve control system under different working conditions are analyzed theoretically,and a simulation model is established in AMESim to verify the control method and characteristic analysis.The results show that the electro-hydraulic load sensing system based on speed regulation can provided by the pump source on demand,eliminate the overflow loss,and only have controllable pressure loss.In addition,the flow feedforward can compensate the pressure drop fluctuation caused by the change of flow.Then,two servo valves are used to realize the independent regulation of the inlet and outlet of load sensing system.According to the working condition of the system,the corresponding control strategy is designed to improve the energy efficiency and stability of the system.Under the power condition the position of hydraulic cylinder is controlled by adjusting the spool displacement of the inlet valve,the pressure of the outlet chamber is controlled by adjusting the spool displacement of outlet valve,and the speed of the servo motor is adjusted to realize the load sensing function.Under over-running condition,the position of hydraulic cylinder is controlled by adjusting the spool displacement of the outlet valve,the oil inlet valve is fully open,and the speed of the pump is adjusted to directly control the pressure of inlet chamber.The pressure feedback and speed feedforward control method is used to control the pressure of hydraulic cylinder.The pressure characteristics and energy efficiency of the system under different working conditions are analyzed theoretically,and the simulation model of the load sensing system with independent inlet and outlet is established by AMESim / Simulink joint simulation method,which verifies the front control strategy,control method and characteristic analysis.The results show that the load sensing system with based on independent inlet and outlet can realize decoupling of two orifices.Under the power condition,the pressure of outlet chamber can be controlled at a lower value to reduce the throttle loss of outlet.The pressure of inlet chamber can be controlled at a stable value to avoid cavitation when the oil inlet chamber is too low.In addition,speed feedforward can compensate the pressure fluctuation caused by the change of hydraulic cylinder speed.Finally,aiming at the problem of strong coupling of each subsystem of the load sensing system based on independent inlet and outlet,the active disturbance rejection controller(ADRC)is introduced to improve the control accuracy and robustness of the system.Based on the previous mathematical modeling,the reduced order state space model of the system is established.The pump control pressure ADRC,valve control pressure ADRC and valve control position ADRC are designed respectively.The control performance of ADRC and feedforward PID controller is compared by AMESim / Simulink simulation method.The results show that only need to know very little system information the ADRC can compensate the unknown uncertainties and disturbances,and has better control effect and stronger robustness than the feedforward PID controller.