Simulation analysis of the hydraulic system of the

Simulation analysis of hydraulic system of shield machine

Abstract: the propulsion system is one of the key systems of shield machine. This paper expounds the principle of the hydraulic system of shield machine. The AMESim simulation tool is used to simulate the system. The simulation results show that the conventional pressure control will cause the violent fluctuation of flow, and the conventional flow control will cause the pressure fluctuation, and the pressure flow compound control method can carry out both pressure closed-loop control and flow closed-loop control, so as to reduce the fluctuation of pressure and flow, and achieve the purpose of real-time control of propulsion pressure and propulsion speed

key words: shield machine, propulsion hydraulic system, pressure flow compound control; AMESim simulation

1 Preface

shield tunneling machine is a complex electromechanical system used for underground tunnel excavation. It has the functions of opening and controlling soil cutting, transporting soil ballast, assembling tunnel lining, measuring, guiding and correcting deviation. Shield tunneling machine has been widely used in subway, railway, highway, municipal, hydropower tunnel engineering. It has the advantages of fast excavation speed, high quality, low labor intensity, high safety, and little impact on surface settlement and environment. Compared with the traditional drilling and blasting tunnel construction, it has obvious advantages and good comprehensive benefits

the propulsion system undertakes the jacking task of the whole shield machine. It is required to complete the turning, curve travel, attitude control, deviation correction and synchronous movement of the shield machine, so that the shield machine can move forward along the preset route. It is one of the key systems of the shield machine

considering that the shield tunneling machine has the characteristics of high power, variable load and long-distance power transmission and control, its propulsion system adopts hydraulic system to realize power transmission, distribution and control

aiming at the working condition requirements of shield propulsion hydraulic system, this paper uses AMESim simulation tool to carry out systematic correlation analysis and research. The simulation results are of great significance to the design of the actual system

2 introduction to the principle of the propulsion hydraulic system

the schematic diagram of the shield machine propulsion hydraulic system is shown in Figure 1. Proportional overflow valve 3 regulates the pressure of hydraulic cylinder to achieve pressure control; Proportional speed regulating valve 14 is used to regulate the flow into the system to achieve speed control; The three position four-way solenoid valve 12 realizes the propulsion, retreat and stop states of the propulsion cylinder; Cartridge valve 1 can provide a fast flow channel for the rapid movement of the propulsion cylinder and reduce the pressure loss along the way of hydraulic oil entering the hydraulic cylinder. Cartridge 13 can provide a fast flow channel for the rapid return of the propulsion cylinder and reduce the return resistance of hydraulic oil. The overflow valve 10 can buffer the system. When the hydraulic cylinder is pushed, the oil inlet will be overloaded instantly, so that the overflow valve will be opened immediately to form a short circuit, so that the oil inlet and return circuits will circulate automatically, and the overloaded oil will be buffered; The two position two-way valve 7 can be powered on to unload and repair the hydraulic cylinder in failure and reduce the pressure impact in unloading. The damping hole is used to adjust the opening speed of the cartridge valve, change the static and dynamic characteristics of the cartridge valve, reduce the hydraulic shock, and prevent the pressure shock caused by the unloading of the two position two-way valve 7. The diameter range of damping hole is generally 0.8 ~ 2.5mm

3 simulation analysis of propulsion hydraulic system

3.1 simulation model

during shield propulsion, the cartridge valve 1 of the system is closed, the three position four-way valve 12 is placed in the right position, the hydraulic oil flows into the rod free chamber of the hydraulic cylinder through the proportional speed regulating valve 14 and the three position four-way valve 12, and the rod chamber hydraulic oil flows back to the oil tank through the three position four-way valve 12 and the proportional overflow valve 1. When the shield tunneling, the cartridge valve 1 is opened, the three position four-way valve 12 is placed in the left position, and the hydraulic oil flows into the rod cavity of the hydraulic cylinder to make the cylinder retreat. Set the pressure of the system and regulate the speed of the system through the proportional flow valve and the proportional speed regulating valve. In order to simplify the analysis and facilitate the simulation, cartridge valve 1, cartridge valve 13 and three position four-way valve 12 can be omitted, and the simplified schematic diagram is shown in Figure 2

use AMESim to establish a simplified simulation principle model of the system, as shown in Figure 3. The hydraulic input adopts the constant pressure input model prsec, the hydraulic cylinder as the actuator selects the system model hj010, and the pipeline selects the system hl000[5]. Since AMESim software does not have a proportional speed regulating model valve and a proportional pressure valve model, HCD (hydraulic component design module) is used to establish its HCD model, as shown in Figure 3

when the pressure reaches the set 8.5MPa during simulation, the load speed rises from 0 load speed to 0.001mm/s, which is easy to cause small piston damage and oil leakage, and the load force is set as a constant: 12361n

3.1.1 simulation of open-loop control of propulsion pressure

the flow of the flow valve is set to 11.4l/min, and the pressure valve is 10.5mpa. When the pressure of the hydraulic cylinder reaches 8.5MPa, the load speed rises from 0 to 0.001m/s. The pressure valve is adjusted to 10.5mpa at 100s and 9.0MPa at 200s. Figure 4 shows the pressure diagram and flow curve of the hydraulic cylinder when adjusting the pressure. Among them, curve 1 is the pressure change curve of hydraulic cylinder, and curve 2 is the flow change curve of hydraulic cylinder

Figure 4 pressure and flow curve of hydraulic cylinder when adjusting pressure

when the pressure rises, the speed of hydraulic cylinder fluctuates greatly until the pressure reaches the new pressure set by the pressure regulating valve. When the pressure is reduced, the speed of the hydraulic cylinder will fluctuate greatly until the pressure reaches the new pressure set by the pressure regulating valve. Therefore, the hydraulic cylinder should adjust the pressure slowly to prevent the cylinder speed from changing too much

3.1.2 simulation of open-loop control of propulsion flow

the flow of the flow valve is set to 11.4l/min and the pressure valve is 10.5mpa. When the pressure reaches the set value of 8.5MPa, the load speed rises from 0 to 0.001m/s. The flow valve is adjusted to 11.4l/min at 100s and 5.7l/min at 200s. The load speed is adjusted to 0.0005m/s at 100s and 0.001m/s at 200s. Figure 5 shows the pressure and flow curve of hydraulic cylinder when adjusting the flow. Among them, curve 1 is the pressure change curve of hydraulic cylinder, and curve 2 is the flow change curve of hydraulic cylinder

when the flow is increased, the speed of the hydraulic cylinder rises and fluctuates, and the pressure changes slightly. When the flow is reduced, the speed of the hydraulic cylinder decreases and fluctuates, and the pressure has changed slightly. The slight change of hydraulic cylinder pressure depends on the change of overflow flow of proportional relief valve

draw the fatigue life curve (S-N curve) from Figure 4; With various special fixtures and the simulation results in Figure 5, it can be seen that simple pressure control will cause flow fluctuations, and simple flow control will cause pressure fluctuations. Neither of them can achieve good control effect

3.2 pressure and flow compound closed-loop control mode

in order to realize pressure and flow compound closed-loop control, the following control principles are adopted. Collect and feed back the pressure and flow signals of the hydraulic cylinder respectively. The proportional pressure valve is the main actuator of the pressure and flow compound control. The proportional flow valve realizes the control of the approximate range of flow and provides the flow necessary for the normal propulsion of the hydraulic cylinder and the stable overflow of the proportional pressure valve, as shown in Figure 6

the compound control adopts the inner loop flow closed-loop control and the outer loop pressure closed-loop control. In order to reduce the maximum fluctuation of flow, a threshold controller is added after the pressure closed-loop PID control, and the maximum change of flow can be controlled by setting the threshold. Where p is the required pressure for system control, QV is the flow required for normal propulsion of hydraulic cylinder, and QY is the flow required for stable overflow of proportional pressure valve

the propulsion load speed is input by the slope, which reaches 60mm/min from 0mm/min within 30s. The flow of the flow valve is set as QV + QY = 20l/min, and the pressure valve P is 10MPa, which is adjusted to 9.0MPa at 150s. The pressure curve of the propulsion hydraulic cylinder is shown in Figure 7 and the flow curve is shown in Figure 8 by adjusting the threshold values to 1, 2 and 3 respectively

increasing the threshold can increase the control time of the pressure circuit, but correspondingly increase the flow fluctuation of the system. Reducing the threshold can significantly reduce the fluctuation of system flow when cyclic stress is applied to the data, but it will increase the control time of system pressure. However, compared with simple pressure or flow control, the fluctuation of pressure and flow has been greatly improved, and the control effect has been significantly improved

4 conclusion

the simulation results show that under the driving condition of shield, the conventional pressure control will cause severe fluctuations in flow, and the conventional flow control will cause fluctuations in system pressure. The pressure flow compound control method can carry out both pressure closed-loop control and flow closed-loop control. At the same time, by adjusting the threshold value, the speed fluctuation of the hydraulic cylinder caused by pressure regulation can be reduced to varying degrees

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