Research On The Characteristics And Control Strategy Of The High Water-based Proportional Directional Valve With Pilot Control By The High-speed Switching Valve

Unmanned fully mechanized coal mining equipment is the development direction of the coal technology revolution.Intelligentization of the hydraulic roof support is an important guarantee for unmanned fully mechanized coal mining face.However,as the key control component of the support,the electro-hydraulic directional valve can not accurately control the valve flow rate,which makes the support unable to accurately adjust its posture,and it is difficult to meet the intelligent development of the hydraulic roof support.Upgrading the existing on-off electro-hydraulic directional valve to the electro-hydraulic proportional directional valve with self-sensing,self-adaptive and programmable control is not only the key to realize the intelligentization of the hydraulic roof support,but also the basis for the unmanned fully mechanized coal face.The hydraulic roof support system uses emulsion as transmission medium and has the characteristics of high working pressure,large flow rate and serious dust pollution.The control valve of the support needs to meet the two-position three-way structure and take into account both manual and electro-hydraulic control functions.The existing water-based proportional valve can’t meet the requirements of coal mine hydraulic support in structure or function.In this paper,based on the traditional displacement-flow feedback principle,the theory is extended,and the novel displacement-flow feedback principle is put forward.The novel displacement-flow feedback principle inherits the advantages of the traditional displacement-flow feedback principle,such as compact structure and reliable performance.By adding control chamber,pilot valve and changing the valve spool structure,the control range of the valve is improved,and it has the functions of manual switch and electro-hydraulic proportional control.On this basis,a new scheme of high water-based proportional directional valve suitable for coal mine hydraulic roof support system is conceived,which uses two pilot valves to cooperate to control the movement of two main valve spools,thus realizing the two-position three-way function of the proportional valve.The pilot stage consists of a 2/3 on-off valve integrated with manual control function and a high-speed switching valve controlled by pulse width modulation(PWM).The main stage is a plug-in structure consisting of inlet/outlet valve spool,valve seat and valve sleeve.The high-speed switching valve and the displacement feedback groove arranged at the end of the inlet valve spool together form a hydraulic control bridge.By changing the duty cycle of PWM signal,the pressure of the hydraulic bridge flow and the inlet valve spool displacement can be controlled,so as to achieve the purpose of proportional control.The flow field and flow characteristics of proportional valve cavity are studied by CFD simulation and flow field test method.Two different cone slide valve structure schemes are visually compared and analyzed.The cone slide valve with the structure of first sealing and then throttling is obviously superior to the cone slide valve with the structure of first throttling and then sealing in key characteristics such as the flow field distribution and the valve spool axial force,and the correctness of the simulation was indirectly verified by experiments.Through the flow field simulation under all working conditions,the nonlinear flow force and the valve flow characteristics were obtained,which could provide some reference for the establishment of simulation model.The main valve displacement control characteristics of the proportional directional valve were studied,and the proportional control law of spool displacement was proved.The proportional control mathematical model of the proportional directional valve was established.The steady-state displacement of the inlet valve spool is approximately inversely proportional to the input duty ratio of high-speed switching valve.And the theoretical basis of stability and frequency response of spool control was obtained.The dynamic and static simulation model of the proportional valve was built,and the manual and proportional control functions were verified.The effects of displacement feedback groove width,valve spool area ratio,liquid supply pressure and valve port pressure difference on valve characteristics were analyzed.The characteristics of complex pilot hydraulic resistance network of the proportional directional valve are studied.By studying the damping characteristics of the pilot hydraulic resistance network in low viscosity medium,the key size parameters such as displacement feedback groove,annular leakage gap at the feedback groove,return fluid resistance and their matching rules are determined.The flow-pressure characteristics at the displacement feedback groove were obtained by means of flow field simulation,and the main regulation and control function of the feedback groove on the pilot liquid flow under reasonable pilot liquid resistance parameters was verified.The pilot flow demand under the theoretical equilibrium pressure was obtained,which provided the basis for the selection and design of high-speed switching valve.The coupling law of the effect of discontinuous pilot flow control on the main valve control chamber and spool displacement was proved.By increasing the PWM carrier frequency,the pressure pulsation of the control chamber and the oscillation amplitude of the spool can be reduced.In order to make up for the shortcomings of the proportional valve,such as poor linearity of spool displacement control,large hysteresis and small load stiffness,a facing model uncertainty adaptive robust control strategy for the proportional valve was proposed.The adaptive robust strategy mathematical model of the proportional valve was established,and the corresponding control simulation model was built according to the control algorithm.The adaptive robust control strategy can effectively improve the control characteristics of the valve.And the response speed of the valve spool is effectively improved.Under different signal inputs,there is no obvious difference in the response speed of the valve spool.The linearity and hysteresis characteristics of valve spool are significantly improved,and at the same time,the valve spool displacement control has better resistance to load change.Based on the characteristics of valve port flow,the control method of the programmable proportional valve for valve flow was proposed through the nonlinear compensation control strategy of the valve flow.The valve flow has good follow-up with the input signal.The valve can adaptively adjust the opening of the valve port when the load pressure changes,which ensures the stability of the valve port flow.Based on the programmable control technology of the proportional valve,the proportional valve cylinder control system of the hydraulic roof support was constructed.The purpose of controlling the stroke and speed of the hydraulic cylinder is achieved by controlling the valve flow.In this paper,the design and processing of the proportional directional valve prototype and controller were completed.At the same time,the proportional valve test system was built.A series of confirmatory tests were carried out on the proportional directional valve.In the sealing test of the valve port,the sealing between the inlet/outlet valve spool and the valve seat is reliable and leak-free.Under manual operation,the switch control is smooth without jamming.And under the electro-hydraulic proportional control,the change rule of the response speed and the steady-state displacement is consistent with the theoretical and simulation research.Be worthy of special mention,there is a lag phenomenon in the starting moment of the valve spool,and the larger the duty cycle,the longer the lag time.Through the adaptive robust control strategy of the proportional valve,the start lag phenomenon of the spool step response is eliminated.The load stiffness of spool displacement control is improved,and the steady-state displacement of the spool is the same under different load pressures.At the same time,the linearity of spool displacement and hysteresis characteristics are greatly improved.The research results and methods of this thesis can provide technical reference for the design and improvement of proportional directional valve of the hydraulic roof support,and lay the foundation for the development of intelligent technology of the hydraulic roof support.