Design and Experimental Research on the hydraulic

Design and experimental research of shield propulsion hydraulic system

Abstract: shield is a kind of technology intensive major engineering equipment that integrates mechanical, electrical, hydraulic, measurement and control and other multidisciplinary technologies and is dedicated to the excavation of underground tunnel engineering. The propulsion system is the key system of the shield, which mainly undertakes the jacking task of the shield, and requires the completion of the functions of the shield, such as turning, curve travel, attitude control, deviation correction and synchronous movement. Using electro-hydraulic proportional control technology, a shield tunneling hydraulic system with pressure flow compound control is designed, and its working principle and system composition are described in detail. The control of the propulsion pressure and speed of the propulsion hydraulic system is studied on the shield simulation test-bed. The test results show that the designed propulsion hydraulic system can control the propulsion pressure and speed in real time, and meet the working needs of the shield under different geological conditions

shield is a kind of technology intensive major engineering equipment that integrates multi-disciplinary technologies such as machinery, electricity, hydraulics, measurement and control, and is dedicated to the excavation of underground 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. In the tunnel construction of soil stratum with complex geological conditions, high groundwater level and large buried depth and geological stratum dominated by soil, the better construction method is shield construction [1]

the propulsion system is the key system of the shield, which mainly undertakes the jacking task of the shield, and requires the completion of the functions of the shield, such as turning, curve travel, attitude control, deviation correction and synchronous movement

the control objective of the propulsion system is to carry out stepless coordinated adjustment of the propulsion speed and pressure according to the soil quality of different construction strata and the changes of their earth pressure on the premise of overcoming the propulsion resistance encountered in the process of shield propulsion, so as to effectively control the surface settlement, reduce the surface deformation, and avoid unnecessary over excavation and under excavation. Generally speaking, the control technology of shield propulsion system in foreign countries is relatively advanced, but the key technology is confidential. There are still disputes about the control of imported or self-developed shield propulsion system in China. Generally, force control system is mainly used, and some are mainly speed control system. However, a single pressure control will cause flow fluctuations, resulting in the instability of the shield propulsion speed; A single flow control will cause pressure oscillation, making the propulsion pressure of the hydraulic cylinder inconsistent, which will aggravate the soil disturbance and increase the surface deformation [2, 3]. Therefore, a single pressure control or flow control is difficult to meet the complex control requirements of the shield under nonlinear variable load conditions. Based on this, we designed a propulsion hydraulic system based on pressure flow compound control, and carried out relevant experimental analysis

1 design of shield propulsion hydraulic system

the power transmission and control system of shield has the characteristics of large transmission power, variable load, complex movement, high reliability requirements, small installation space and poor working environment. The inherent characteristics of hydraulic transmission and control system can just meet the needs of shield

1.1 principle of propulsion hydraulic system

the shield propulsion hydraulic system is generally composed of main drive pump, hydraulic control valve, propulsion hydraulic cylinder and hydraulic pipeline. The propulsion hydraulic cylinder is installed at the rear of the diaphragm of the seal chamber and evenly distributed along the circumference of the shield. It is the actuator of the propulsion system. The propulsion system is provided with high-pressure oil by the main drive pump placed at the tail of the shield, and various functions are realized through the control of various hydraulic valves

the structural diagram of the shield propulsion system is shown in Figure 1. Six hydraulic cylinders are used as the actuator of the propulsion system, which are symmetrically distributed left and right. Each hydraulic cylinder is equipped with a magnetostrictive displacement sensor, which can measure the propulsion displacement of the hydraulic cylinder in real time

the propulsion hydraulic system adopts variable pump on the main oil circuit to realize pressure adaptive control; For the six actuator hydraulic cylinders, the control mode of the actual shield is simulated, and they are divided into six groups for group control. The control modules in each group are the same, which are composed of proportional overflow valve, proportional speed regulating valve, electromagnetic directional valve, auxiliary valve and related detection elements. Figure 2 is the working principle diagram of the propulsion hydraulic system

when the shield is advancing, the two position four-way solenoid directional valve 10 is powered on, the two position two-way solenoid directional valve 1 is powered off, and the system supplies oil through the proportional speed regulating valve 2. At this time, the three position four-way solenoid directional valve 9 is switched to the working state B position, and the piston rod of the hydraulic cylinder 6 moves forward. During the propulsion process, the built-in displacement sensor 7 in the hydraulic cylinder 6 detects the propulsion displacement in real time, converts it into an electrical signal and feeds it back to the proportional electromagnet of the proportional speed regulating valve 2 to control the opening of the throttle port in the proportional speed regulating valve 2, so as to realize the real-time control of the propulsion speed. At this time, the excess flow in the system can flow out of the proportional overflow valve 3. In order to find the most perfect seat cushion adjustment in posture, the propulsion pressure must also be controlled in real time. At this time, the pressure sensor 5 can detect the propulsion pressure of hydraulic cylinder 6, convert it into an electrical signal and feed it back to the proportional electromagnet of proportional relief valve 3, and control the throttle opening of proportional relief valve 3. The proportional overflow valve 3 and the proportional speed regulating valve 2 in the grouping together with the pressure sensor 5 and the displacement sensor 7 form a pressure flow composite control, which can control the propulsion pressure and speed of the propulsion system in real time, and meet the requirements of the propulsion pressure

and the propulsion speed that change at any time during the shield propulsion process [4]

when it returns quickly, the two position two-way electromagnetic directional valve 1 is powered on, and the proportional speed regulating valve 2 is short circuited. The system adopts large flow oil supply. At this time, the three position four-way electromagnetic directional valve 9 is switched to the working state a position, and the piston rod of hydraulic cylinder 6 returns quickly to meet the requirements of segment assembly

the hydraulic lock 8 is combined with the three position four-way electromagnetic directional valve 9 with Y-type intermediate function to form a locking circuit, which can well prevent the leakage of hydraulic oil when the intermediate stop. When the hydraulic cylinder retreats, the balance valve 4 can play a role in making the movement stable

when multiple hydraulic cylinders act at the same time, the two position four-way solenoid directional valve 10 is powered off, and the main oil circuit is temporarily disconnected. After the control signals of multiple hydraulic cylinders are in place, the two position four-way solenoid directional valve 10 is powered on, and the main oil circuit is connected, so that multiple hydraulic cylinders work at the same time

1.2 propulsion hydraulic system pump station integration

according to the different structural forms and cooling methods of the hydraulic power pump station, the propulsion hydraulic system adopts the air-cooled vertical assembly structure, and the air cooler, motor and main drive pump are installed under the oil tank, which is not only conducive to the heat dissipation of the system, but also makes the oil tank unit of the pump station compact and saves installation space. Figure 3 shows the pump station of the propulsion hydraulic system. Considering that the six hydraulic cylinders in the propulsion system are symmetrically distributed left and right, the integrated valve block is used to integrate the control hydraulic valves in the group. The integrated valve blocks of each group are distributed nearby and installed at the rear end of the propulsion system, close to the rodless cavity of the hydraulic cylinder. Figure 4 shows the distribution of integrated valve blocks in each group of the propulsion hydraulic system. The inlet and outlet oil pipelines of the six grouped integrated valve blocks on both sides are integrated into the oil inlet pipeline and return pipeline through the oil distribution valve block, which are connected to the pump station of the propulsion system

2 analysis of propulsion control test

this test is carried out on the shield simulation test bench, which is composed of a shield with a diameter of 1.8 m and a simulated soil box with a length of 8.6m. The shield is driven forward by the propulsion hydraulic system; The simulated soil box adopts the method of bag pressurization to simulate the excavation at the depth of 10 m underground. During the test, the total distance of propulsion in the typical soil stratum of clay is 240 cm. According to the test time, two sections of 80 ~ 140 cm and 140 ~ 240 cm are selected to carry out relevant test analysis on the propulsion pressure and speed

figures 5 and 6 are the propulsion speed and pressure curves of a single grouped hydraulic cylinder during speed regulation. The test is carried out in the range of 80 ~ 140cm of the propulsion distance. The No. 4 hydraulic cylinder is selected. At the beginning of the test, adjust the speed regulating knob on the control panel to adjust the propulsion speed to 30 mm/min. after 200 s, continue to adjust the speed knob counterclockwise to adjust the speed to 42 mm/min

it can be seen from Figure 5 that during the adjustment of the shield propulsion speed from 0 to 30 mm/min, the speed has an overshoot, and the maximum speed reaches 40 mm/min in about 10 s. This is because the front load in the propulsion process is soft soil. If the soil is assumed to be a viscoelastic system, its stiffness and viscosity are relatively large, which is an important factor affecting the propulsion speed; In addition, the moving part of the shield has large mass and inertia, so the response is also slightly slower. When the speed is adjusted in 200 s, the propulsion speed is changed from the original speed of 30 mm/min to 42 mm/min, realizing the speed adjustment. However, due to many unforeseen factors, the propulsion speed will fluctuate within a certain range

Figure 6 shows the pressure curve of hydraulic cylinder propulsion. When the shield starts tunneling, the pressure is relatively large, and then there is a process of reduction and gradual stability. This is because when the shield starts tunneling, it needs to overcome the static friction of the shield and the inertia of the moving part of the shield. After the tunneling starts, the system has only dynamic friction. At this time, the speed of the shield inertia system exceeds the set speed, so the pressure of the hydraulic cylinder decreases, and finally reaches stability. When the propulsion speed is adjusted in 200 s, the propulsion speed can well follow the adjustment signal. However, at this time, the propulsion pressure fluctuates, and the average value of the fluctuation is larger than that before the adjustment. This is because the propulsion speed needs to rise, and the hydraulic cylinder must provide greater thrust. Only with greater thrust can the acceleration of the shield be increased and the speed of the shield be increased. When the speed reaches the set value, the pressure drops and finally stabilizes within a certain range

Figures 7 and 8 are the curves of propulsion pressure and propulsion speed introduced by the company of hydraulic cylinders in a single group during pressure regulation. The test was also carried out in the range of 80 ~ 140 cm, and the No. 3 hydraulic cylinder was selected. At the beginning of the test, adjust the pressure regulating knob on the control panel, and start the pressure regulating test after 100 s. according to the loading condition, adjust the propulsion pressure of No. 3 hydraulic cylinder from 4 MPa to 7.5 MPa. It can be seen from Figure 7 that the pressure of the propulsion system has an overshoot when the pressure is adjusted at 100 s, and the propulsion pressure gradually reaches a stable state after about 170 s. When the pressure is adjusted in 100 s, the propulsion pressure can basically follow the adjustment signal. At this time, the propulsion speed of the hydraulic cylinder has an instantaneous increase process. This is because if the propulsion pressure wants to rise, the system must provide greater flow to increase the acceleration of the propulsion system. When the pressure reaches the set value, the propulsion speed gradually decreases and finally stabilizes in a small range

Figures 9 and 10 are the propulsion pressure and propulsion speed curves of hydraulic cylinders in two left-right symmetrical groups during pressure regulation. The test was carried out in the range of 140 ~ 240 cm. Two hydraulic cylinders, No. 2 and No. 5, were selected, and the pressure regulation test was started in 50 s. From the propulsion pressure test curve in Figure 9, it can be seen that due to the slow response speed of the shield, the propulsion pressure reaches a stable state in about 120 s; In addition, due to the uneven pressure on the bag in the simulated soil box, the stress level of the soil directly in front of the cutterhead excavation face is also different. At this time, the pressure of No. 2 cylinder is stable at about 5.5 MPa, while the pressure of No. 5 cylinder is stable at about 6.5 MPa. It can be seen from the propulsion speed test curve in Figure 10 that when the system adjusts the pressure, the propulsion speed of the hydraulic cylinder does not fluctuate much, and the original setting is still maintained