Accurate posture control of hydraulic roof supports, which use pressurized water as their fluid power source, is an important part and research direction of intelligent fully mechanized mining face. At present, the large flow on/off directional valve used on the hydraulic roof support cannot meet the requirement of precise posture control of the roof support. To overcome the conundrum, a novel two-position three-way electro-hydraulic proportional directional flow valve for hydraulic roof support is proposed. The new valve contains two pilot stages and two main spools. The two pilot stages cooperate with each other to control the movement of the two main valve spools, which are the inlet valve spool and the outlet valve spool. The inlet valve spool adopts the Valvistor principle. The valve can realize manual pilot control and electro-hydraulic proportional flow control of the passage P-A, which has been verified by a simulation model. In this paper, the static and dynamic mathematical models of the new proportional valve are established, and the key parameters affecting the valve performances are analyzed and verified by the simulation model. An optimization control scheme is proposed to overcome the influence of supply pressure, P-A pressure difference, and nonlinear interference force on steady-state displacement and response speed of the valve. The results show that this optimization method can significantly improve the response speed of the spool and promote the linearity of spool displacement under a slope signal. In addition, the fluctuation of chamber pressure and spool displacement caused by the discontinuous flow of a fast switching valve is systematically analyzed. The analysis shows that increasing pulse-width modulation carrier frequency is an effective way to reduce fluctuation amplitude. The research provides a new design idea and control method for an electro-hydraulic proportional directional valve of hydraulic roof support.
In the field of fully mechanized coal mining equipment, the hydraulic valve used in the hydraulic support is an on/off directional valve. There are many problems caused by the valve such as large pressure shock and discontinuous flow control. Therefore, a novel two-position three-way hydraulic proportional valve suitable for high-pressure and large-flow conditions is proposed to overcome the above problems. The novel valve utilizes a two-stage structure and the displacement follow-up principle is adopted between the pilot stage and the main stage to meet proportional control. In this paper, a simulation model of the novel proportional valve was established after a simplified analysis of the structural principle. Its reliability and the feasibility of the design were verified by the test results under different working conditions. Then, the step response characteristics of the proportional valve under different strokes were predicted and analyzed. Nonlinear characteristics were presented, and the closing time was shorter than the opening time because of the influence of nonlinear flow force. Under different ramp signals, the displacement of the main inlet spool was always approximately equal to the displacement of the pilot stage. Then, the motion relationship between the pilot stage and the main stage was studied, and the influence of the structural parameters on the stability was analyzed.
The 1000 L/min large flow hydraulic system for the hydraulic support used in a coal mine is currently a topic of great interest. The large flow directional valve is a key component for hydraulic systems, so the design of the 1000 L/min large flow directional valve is essential. The designed single-channel valve shows serious hysteresis characteristics in a 1000 L/min large flow condition, but it does not happen in a 16 L/ min small flow condition. Based on this phenomenon, the computational fluid dynamics (CFD) technology was used to simulate the flow in the valve. It was discovered that the single-channel caused unbalanced pressure in the annular region and on the surface of the valve spool, so the valve spool is subjected to great radial unbalanced force. Then a double-channel valve was designed to improve the pressure distribution. The simulated radial unbalanced force on the double-channel valve is 67.2% lower than that of the single-channel valve. The experimental results showed that the hysteresis characteristics also disappeared under the 1000 L/min large flow condition. Therefore, the conclusion can be drawn that the hysteresis characteristics of the single-channel valve is due to the radial unbalanced force caused by the unsymmetrical flow field. The results show that the maximum radial unbalanced force the valve spool can withstand is 170 N. Furthermore, symmetrical flow passages have to be taken into account in large flow conditions. This paper provides valuable references for the design of large flow valves.
The large flow electro-hydraulic directional valves are the key operating components for automation of the hydraulic roof supports in the coal mine. Cracking is a common failure mode of the valve. Effects of the buffer damp diameter, the valve type and the static pressure on the stress of the valve were researched. The valve dynamic behavior was investigated by AMESim. The transient collision stresses of the inlet valve sleeve of the main control valve under different buffer damp diameters and different valve types were investigated by ANSYS/LS-DYNA. The static stress analysis was conducted in ANSYS too. Results show that the valve failure is due to the fatigue of the inlet valve sleeve when suffered from the collision stress wave in the valve opening process, rather than the lack of component strength. The buffer damp diameter, the key parameter of the valve, has a significant effect on the collision stress of the inlet valve sleeve. The integrated type valve has a better stress state compared to the separated type valve. This paper provides an effective method to solve the fracture problems of hydraulic directional valves. It is also significant for the design and optimization of hydraulic components.
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