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关键词：: 采用采取采纳单向阀平衡回路实验试验装置设计

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摘要

液压基本回路是为了实现特定的功能把有关的液压元件组合起来的典型油路结构，是组成任何液压系统的基础。平衡回路的功用就是在于防止垂直或倾斜放置的液压缸和与之相连的工作部件因自重而自行下落，使执行元件的回油路上保持一定的背压值来平衡工作的稳定。本文对采用液控单向阀的平衡回路实验装置的原理进行了详细的分析，再根据液压传动相关理论进行数据计算，设计液压缸，选择合适的液压元件、液压油箱、液压站的动力装置，然后确定电机与泵的安装方式，进行管路与管接头的选择等等，最后对本次设计的实验台装置进行性能验算，包括压力损失的验算、总统效率估算和系统温升校核三个环节。同时完成设计的总装配图及部分零件图等等，最终完成整个设计。

关键词：液压；液压回路；平衡回路；实验台

The design of experimental device adopts the hydraulic control one-way valve balance circuit

Abstract

The hydraulic pressure basic circuit is to put the typical circuit structure of hydraulic components are combined on the realization of specific functions, is the basic component of any hydraulic system. Balance circuit function is to prevent the hydraulic cylinder vertically or obliquely placed and connected with the working parts caused by self weight drop, so that the implementation of components of the return line to maintain a certain pressure to balance the work stability. The principle of balance circuit experiment device of the hydraulic control one-way valve are analyzed in detail, and then the related theory of data according to the calculation of hydraulic transmission, hydraulic cylinder design, selection of hydraulic components, power device, hydraulic station hydraulic oil tank right, then determine the installation mode of motor and pump, pipeline and pipe joint selection and so on, the performance calculation of the design of the experimental device, including temperature checking, President efficiency estimation and the pressure loss of the system or check three links. At the same time to complete the design of assembly drawing and parts drawing and so on, and ultimately complete the design.

Key Words: Hydraulic pressure; Hydraulic pressure circuit; balance circuit ; laboratory stage

1 绪论1

1.1综述1

1.2题目背景1

1.3研究意义1

1.4国内外相关研究情况1

1.5主要研究内容2

2 液压系统的设计分析3

2.1液压系统组成3

2.2系统的设计要求及流程3

2.3回路原理的设计4

2.3.1平衡回路4

2.3.2回路中个元件的作用4

2.3.3采用液控单向阀设计的平衡回路4

2.4工况分析5

2.5系统方案设计5

3 液压缸的设计6

3.1预选系统设计压力6

3.2液压缸主要结构尺寸6

3.2.1液压缸内径D和活塞杆直径d的确定6

3.3液压缸的结构设计9

3.3.1缸体与缸盖的连接形式9

3.3.2活塞杆与活塞的连接结构10

3.3.3活塞杆导向部分的结构10

3.3.4活塞及活塞杆处密封圈的选用11

3.3.5液压缸的安装连接结构11

4 液压站的设计12

4.1液压泵装置12

4.1.1液压泵设计选型12

4.2液压油箱的设计14

4.2.1液压油箱有效容积的确定14

4.2.2液压油箱的外形尺寸15

4.2.3液压油箱组件结构设计15

4.3液压控制装置16

5 液压辅件的选择18

5.1油管18

5.1.1油管的布局要求18

5.1.2油管的选用计算18

5.2管接头19

5.3液压油19

5.4实验台结构设计20

5.4.1实验台组件台面设计20

5.4.2安装面板设计20

6 液压系统的性能验算21

6.1压力损失的验算21

6.1.1工作进给时进油路压力损失21

6.1.2工作进给时回油路压力损失22

6.2系统温升的验算22

7 液压系统的安装调试与维护24

7.1液压系统的安装24

7.1.1液压元件的检查24

7.1.2液压元件和管道的安装24

7.2液压站的使用与检查25

7.2.1使用注意事项25

7.2.2操作方法25

7.2.3检查25

8 总结26

致谢27

参考文献28

毕业设计（论文）知识产权声明29

毕业设计（论文）独创性声明30

附录31

1 绪论

1.1综述

液压传动是利用有压液体作为传动介质来传递动力或控制信号的一种传动方式，也是利用有压液体的压力进行能量传递、能量转换和能量控制的传动系统。它由能源装置、传动装置、辅助装置和执行元件组成。传动部分是机械装置的重要组成部分，起着传递运动和力的作用。传动装置的选择正确与否直接决定着实验台的性能好坏；传动方案的选择要充分发挥液压传动的优点，力求设计出结构简单、工作可靠、效率高、成本低、操作简单、维修方便的液压传动系统。

1.2题目背景

液压传动与控制是现代机械工程的基础技术，由于其在功率质量比、无级调速、自动控制、过载保护等方面的独特技术优势，使其成为国民经济中各行业、各类机械装备实现机械传动与控制的重要技术手段。特别是20世纪90年代以来，新兴产业不断涌现，并与现代电子与信息相结合，进一步刺激和推动了液压技术的发展，使其在国民经济各行业获得广泛应用。正确合理地设计和使用液压系统，对于提高各类液压机械设备及装置的工作品质和技术经济性能具有重要意义[1]。

1.3研究意义

本课程的学习目的在于学生综合使用《液压与气压传动》等专业课程的理论知识和生产实际知识，进行液压试验装置的设计实践，使理论知识和生产实际知识紧密结合起来，从而使这些知识得到进一步的巩固、加深和扩展。

通过该题目原理图的设计，可以使学生熟悉液压传动系统设计的一般程序，了解并掌握液压传动这门技术，掌握机械设计的一般程序和基本方法。总之，通过本题目的设计，可以使机械设计制造及其自动化专业的学生对四年所学课程得到一次较为全面的实践锻炼。

1.4国内外相关研究情况

由于液压技术广泛应用了高技术成果，如自动控制技术、计算机技术、微电子技术、磨擦磨损技术、可靠性技术及新工艺和新材料，使传统技术有了新的发展，也使液压系统和元件的质量、水平有一定的提高[2]。综合国内外专家的意见，其主要的发展趋势将集中在以下几个方面：

a. 减少能耗，充分利用能量液压技术在将机械能转换成压力能及反转换方面，已取得很大进展，但一直存在能量损耗，主要反映在系统的容积损失和机械损失上。如果全部压力能都能得到充分利用，则将使能量转换过程的效率得到显著提高。

b. 主动维护液压系统维护已从过去简单的故障拆修，发展到故障预测，即发现故障苗头时，预先进行维修，清除故障隐患，避免设备恶性事故的发展。另外，还应开发液压系统自补偿系统，包括自调整、自润滑、自校正，在故障发生之前，进市补偿，这是液压行业努力的方向。要进一步引发液压系统故障诊断专家系统通用工具软件，对于不同的液压系统只需修改和增减少量的规则[3]。

c. 机电一体化电子技术和液压传动技术相结合，使传统的液压传协与控制技术增加了活力，扩大了应用领域[7]。实现机电一体化可以提高工作可靠性，实现液压系统柔性化、智能化，改变液压系统效率低，漏油、维修性差等缺点，充分发挥液压传动出力大、贯性小、响应快等优点。

产品向体积小、重量轻、功耗低、组合集成化方向发展，执行元件向种类多、结构紧凑、定位精度高方向发展；气动元件与电子技术相结合，向智能化方向发展；元件性能向高速、高频、高响应、高寿命、耐高温、耐高压方向发展，普遍采用无油润滑，应用新工艺、新技术、新材料[4]。

1.5主要研究内容

平衡回路的功用就是在于防止垂直或倾斜放置的液压缸和与之相连的工作部件因自重而自行下落，使执行元件的回油路上保持一定的背压值来平衡工作的稳定。本文设计的采用液控单向阀平衡回路的实验台装置，主要工作有：

(1) 研究采用液控单向阀+单向节流阀的平衡回路的原理；

(2) 设计出合理的、能满足使用要求的平衡回路实验装置；

(3) 采用液压缸加载；

(4) 绘制主要零件图；

(5) 选择液压元件型号；

(6) 对系统进行温升校核。

2 液压系统的设计分析

2.1液压系统组成

液压系统主要由以下五个主要部分来组成：

a. 能源装置：液压泵。它将动力部分（电动机）所输出的机械能转换成液压能，给系统提供压力油液。

b. 执行装置：液压机（液压缸、液压马达）。通过它将液压能转换成机械能，推动负载做功。

c. 控制装置：液压阀。通过它们的控制和调节，使液流的压力、流速和方向得以改变，从而改变执行元件的力（或力矩）、速度和方向，根据控制功能的不同，液压阀可分为压力控制阀、流量控制阀和方向控制阀。压力控制阀又分为益流阀(安全阀)、减压阀、顺序阀、压力继电器等；流量控制阀包括节流阀、调整阀、分流集流阀等；方向控制阀包括单向阀、液控单向阀、梭阀、换向阀等。根据控制方式不同，液压阀可分为开关式控制阀、定值控制阀和比例控制阀。

d. 辅助装置：油箱、管路、蓄能器、滤油器、管接头、压力表开关等.通过这些元件把系统联接起来，以实现各种工作循环。

e. 工作介质：液压油。绝大多数液压油采用矿物油，系统用它来传递能量或信息。

2.2系统的设计要求及流程

液压的设计一般泛指液压传动系统设计。由于液压传动系统和液压控制系统从结构和工作原理而言，并无本质上的区别。通常所说的液压系统设计，皆指液压传动系统设计。液压系统的设计与主机的设计是紧密联系的，当从必要性、可行性和经济性几方面对机械、电气、液压和气动等传动形式进行全面比较和论证，决定应用液压传动之后，二者往往同时进行[5]。所设计的液压系统首先应满足主机的拖动、循环要求，其次还应符合结构组成简单、体积小重量轻、工作安全可靠、总体看来，液压系统设计的流程是：

a. 明确系统的设计

b. 分析系统工况

c. 确定主要参数

d. 拟定液压系统原理图

e. 选择液压元件

f. 验算液压系统性能

g. 绘制工作图编织技术文

2.3回路原理的设计

液压系统的设计可分为两大步骤：一、液压系统的原理及性能设计；二、液压系统的技术设计(液压装置的结构设计即液压站的设计)。液压站按照动力源与控制装置是否安装在一起，可分为整体式液压站和分离式液压站。一个液压系统能否可靠有效地运行，在很大程度上取决于液压站结构选型是否合理及设计质量的优劣，设计时必须给予足够重视[6]。

2.3.1平衡回路

为了防止立式放置的液压缸活塞，因为垂直运动工作部件的重力而自行下滑，或在工作部件下行时速度失控这种现象发生，往往在液压系统中设置能产生一定背压的液压元件，以保证活塞在任意位置上被锁定，并且可以控制工作部件的下落速度，这样的液压回路称为平衡回路。其作用就是防止立式安装的液压缸受负载力或重力的作用自行下落，或者下落时出现超速失控现象等，它对于保证液压系统的安全性等方面起到了重要作用。

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内容简介：: 毕业设计（论文）中期报告题目：采用液控单向阀的平衡回路实验装置设计系别机电信息系专业机械设计制造及其自动化班级姓名学号导师 2013年 3 月 22 日设计（论文）进展状况（1）查阅资料并完成一篇3000字以上的关于液压系统的外文翻译：盾构机的压力调节液压系统的仿真分析。（2）回路采用了液压缸加载，对原理图进行了进一步的完善，具体如下图所示。（3）通过初步计算，基本完成方案设计。主要完成了液压元件的初步估算，管道以及管接头的初选，油箱的尺寸选择，液压缸的设计以及各个零部件的选择。具体所选液压元件的型号规格如下表。表1 液压元件明细表序号名称型号额定流量（Lmin）调定范围（MPa）其它1单叶片定量泵YB1-10152电动机Y-90S-2三相异步电动机额定功率1.1Kw，额定转速1400r/min3滤油器（线隙式）XU-J168016通径12mm4溢流阀YF3-10B630.56.3重量1.6kg5液控单向阀YAF3-10B636单向阀AF3-Ea10B407减压阀JF3-10B630.56.3重量2.85kg8节流阀LF3-E10B100重量4kg9二位四通电磁换向阀24F3-10B6010三位四通电磁换向阀34F3-10B60表2 液压缸和油箱设计的基本尺寸液压缸：最大外负载F=3000N，工作腔压力P1=2.0Mpa，回油腔背压P2=0.2Mpa，缸内径D=50mm，活塞杆径d=25mm，液压缸的最大流量为10.3L/min。油箱：液压油箱的有效容积V=30L，计算选得BEX系列液压油箱，型号为BEX-63A，长：宽：高=550：450：600。（4）进入技术设计阶段：装配图（包括：实验台总装配图，背后油道管路图），和零件图（包括实验台焊接支架构成图，油箱焊接组件图，液压缸零件图以及其他各部分零件图）。现已基本完成了实验台总装配图的绘制和一些零件图的绘制等。装配图如下图所示。存在问题及解决措施（1）在管道选取上考虑不够全面，选择了可用于低压系统的尼龙管。解决的方法是也要考虑其连接时的美观度，所以选择钢管。（2）在原理回路中工作缸和加载缸两活塞杆之间的连接不太完善，不能很好的实现回路动作。解决的方法是在两活塞杆之间应用连接器将二者连接以增加工作时运动的连贯性，使回路运行更加有效。（3）在实验台装配图、立式泵安装部分的绘制上，会出现一些不合理之处，在老师的悉心指导下正在逐步一一改进。（4）液压缸的设计是否还需要加装缓冲装置和排气装置，加装对液压缸的安装形式是否有影响。解决的方法是由于此次实验装置系统设计属于低压系统，先暂时按不加处理，液压缸选取底面脚架安装形式、进出油口选螺孔连接，最后校核时再进一步详细分析。后期工作安排后期的工作安排：后期的主要工作重点还是放在工程图的绘制，并且进一步完善装配图、加紧时间完成所有零件图的绘制。并同时撰写论文，最后对整个油路进行热温升校核，完成全部技术设计。后期的时间安排如下：911周完成全部技术设计并校对所有图的绘制；1213周撰写毕业设计论文；14周，答辩前准备。指导教师签字：年月 RESEARCH ARTICLEZhibin LIU, Haibo XIE, Huayong YANGSimulation analysis of pressure regulation of hydraulic thrustsystem on a shield tunneling machine Higher Education Press and Springer-Verlag Berlin Heidelberg 2011AbstractHydraulic thrust system is an important systemin a shield tunneling machine. Pressure regulation of thrustcylinders is the most important function for thrust systemduring tunnel excavation. In this paper, a hydraulic thrustsystem is explained, and a corresponding simulation modelis carried out in order to study the system characteristics.Pressure regulation of a certain groups cylinders has littleinfluence on regulation of the other groups cylinders. Theinfluence will not affect the process much during tunnelexcavation. Pump displacement may have a greater effecton pressure regulation and oil supply flow rate should beadaptive to the systems demand. A exacting situation issimulated to explain how pressure regulation works duringtunnel excavation.Keywordstunnel, hydraulic thrust system, pressureregulation, simulation1IntroductionA shield tunnel machine is a large and complex machineused in underground tunnel excavation. It is used inconstruction projects such as underground rail lines, urbanpipelines, submarine tunnels, and so on. Hydraulictechnique is widely applied in a shield tunneling machine.For instance, it is used in the thrust system, the cutter headdrive system, the screw conveyor, and the segment erector.Research works about tunnel excavation have beencarried out. Sugimoto and Sramoon built a theoreticalmodel for tunnel excavation based on mechanics analysis1; their simulation results are in good agreement withobserved data 2. Maynar and Rodriguez used a discretenumerical model to analyze the excavation process. Somestudies about thrust force and torque were also carried out3. Xu et al. have discovered some relationship betweenworking parameters during tunnel excavation 4. Only afew studies about the hydraulic system on the machinehave been done. Hu et al. have done some work on a thrustsystem of a machine. Pressure and flow compound controlhave also been researched 5.A different system in Ref. 5 is studied in this research.Pressure regulation of thrust system is studied by using asimplified simulation model and cases of such regulationare discussed.2Thrust systemA thrust system is an important part of a shield tunnelingmachine. The system consists of power units (electricmotor and hydraulic pump), hydraulic valves, andhydraulic cylinders as actuators. The number of thrusthydraulic cylinders is usually 16 or 32. If individualcontrol of hydraulic cylinders is applied, a high number ofproportional control valves and pressure sensors arerequired. Moreover, the machine operator has to control16 or 32 pressure parameters during excavation. Individualcontrol is rather complicated and expensive. Nowadays,thrust cylindersare usually dividedintofour or five groups,with the four-group arrangement more common. Four-group cylinders are divided into Group A, Group B, GroupC, and Group D, corresponding to right zone, lower zone,left zone and upper zone. The proportion of ABCD isusually 4543, as shown in Fig. 1.More cylinders are required in Group B so as to counterthe weight of cutter head and the higher earth pressure inthe lower zone. Oil pressures in different cylinders are thesame if they are in the same group. In this case, only fourproportional control valves are required, and the machineoperator only has to control four pressure parameters.During tunnel excavation, hydraulic cylinders are suppliedwith high-pressure hydraulic oil, which exerts on thesegments to generate a thrust force to push the machineReceived January 28, 2011; accepted June 10, 2011Zhibin LIU, Haibo XIE (), Huayong YANGState Key Laboratory of Fluid Power Transmission and Control,Zhejiang University, Hangzhou 310027, ChinaE-mail: Front. Mech. Eng. 2011, 6(3): 377382DOI 10.1007/s11465-011-0226-yforward. The machine operator may adjust hydraulicpressures of thrust cylinders to achieve steering controland machine posture adjustment. After a thrust process isover, segments will be installed to compose a new ring oftunnel. Meanwhile, thrust cylindersare retracted in order tomake room for those segments. When a segment is located,corresponding cylinders are extended out. These cylindersexert on the segment, supporting the segment with a smallforce to complete the installation process.3Hydraulic circuit and modelingThe hydraulic circuit diagram for the thrust system isshown in Fig. 2. The system mainly consists of a variabledisplacement pump 1, a pressure relief valve 2, adirectional control valve 3, four pressure reducing valves4 and sixteen hydraulic cylinders 7. Pump displacement isproportional to the input signal. A pressure relief valvekicks into action when the system is overloaded, and adirectional control valve is used to control the extensionmotion or retraction motion of cylinders. The pressurereducing valve is the most important component and isused to adjust the hydraulic pressure of the cylinders.When the cylinder is extending, high-pressure oil comesfrom hydraulic pump 1, and then flows through directionalcontrol valve 3, pressure reducing valve 4, check valve 5,on/off valve 6, finally entering the rear chamber ofhydraulic cylinder 7. The back pressure oil flows out ofthe rod chamber of cylinder 7, then through directionalcontrol valve 3 and back into the oil tank. When thecylinder is retracting, oil flows through directional controlvalve 3, then into the rod chamber of hydraulic cylinder 7.The back pressure oil flow out of the rear chamber, thenthrough on/off valve 6, check valve 8, directional controlvalve 3, and finally into the oil tank.Commercial software AMESim is used as the analysistool for the simulation. To simplify the model, two groupsof hydraulic cylinders (typically left zone and right zone)are considered for analysis. By using these two zones, it ispossible to simulate the steering motion of the shieldmachine. The simulation model is shown as Fig. 3. All thehydraulic models are the normal models provided by thesoftware except for the pressure reducing valves. Thevalveis built as a “super-component” by compositing severalnormal models. The valve gives more details about notonly the working parameters but also the internalstructures. A variable displacement pump is applied asproportional displacement control pump as it has the samefunction as that on a working shield machine. The pumpdisplacement is proportional to the input signal.Three kinds of forces are considered in the cylinder loadmodel: earth pressure force, friction, and the force causedby the thrust motion. Earth pressure exerts on the cutterhead and linings of the machine. The pressure forceexerted on the cutter head affects the thrust motion, and thepressure force on the lining can be ignored. The frictionforce on linings of the machine caused by the earthpressure is considerable, accounting for about half or moreof the thrust force. During excavation, however, thepressure force and friction force almost maintain con-stantly. Thus, these two forces are set as constant in themodel. Earth pressure is set by the input signal of the loadmodel, and friction is set in the mass model of cylinder.There is a linear relationship between advancing speed andthrust force, as shown in Fig. 4 4. The black star dotsrepresent the experimental results for a 68% open ratiocutter head, and the white square dots represent the resultsfor 36% open ratio. Each solid line shows the linearrelationship between advancing speed and thrust force.The linear relationship has a good agreement with theobserved data in construction of Line No. 3 in theGuangzhou Metro 6.Fig. 1Arrangement of 4-group hydraulic cylindersFig. 2Hydraulic circuit of thrust system378Front. Mech. Eng. 2011, 6(3): 377382A greater thrust force causes a higher advancing speed.That is because greater force induces a greater feed rate ofcutters, and more soil will be cut off in a fixed timeinterval. The thrust force should be greater than earthpressure exerted on the cutter head together with frictionforce on the lining, in order to push the machine toadvance. If thrust force is not great enough, the machinewill not advance. In Fig. 3, there is a dead band in the loadmodel. The dead band represents the situation in whichthrust force is not great enough to push the machineforward; such a situation is referred to in Ref. 6. Whilethe machine is advancing, an increase of the thrust forcewill cause an increase of advancing speed. This experimentresult is applied to the load model. The orientation ofmachine advance is influenced by the pressure distributionof thrust cylinders so pressure regulation determines theprocession of excavation. The machine operator maycontrol the posture of the machine by adjusting thepressures of cylinder groups. The machine may steer left orright, or advance along a small angle of slope ifcorresponding settings of pressure regulation are given.Normally, at the end of a tunnel excavation, the differencebetween actual tunnel axis and designed tunnel axis shouldbe no more than 20mm. The machine operator will adjustthe machine advancing axis to agree with the designedaxis. As a result, pressure regulation is a very importantfunction during tunnel excavation.4SimulationThe simulation parameters shown in Table 1 are obtainedfrom a shield tunneling machine usedin the construction ofthe Nanjing Metro. The left and right thrust groups areused for simulation, and sixteen hydraulic cylinders arereduced to eight. A 63cc/rev maximum displacementpump should be reduced to 31.5cc/rev. Piston diameter ofa real cylinder is 300mm, and rod diameter is 240mm.Either the left or right thrust group, each of which containsfour hydraulic cylinders, is simplified to one hydrauliccylinder, which has the same work area as the originalcylinder group. As a result, the piston diameter and roddiameter of simulation cylinder are 600 and 480 mm,respectively. When oil pressure is about 8MPa, whichsupplies about 9200kN of thrust force, the machine beginsto move. Reference 7 refers that friction force accountsfor about 53.5%73% of thrust force. Accordingly, frictionforce is set at 6000kN, about 65% of thrust force. Theremaining 3200kN is exerted on the cutter head for tunnelexcavation.4.1Pressure regulationSteering control is simulated in this case. Both hydrauliccylinders are initially set to about 14MPa. The machineadvances straight and is expected to steer left. The pressureof right cylinder (Pright) should be higher than that of theleft (Pleft). Pleftmay maintain at 14MPa. Prightis set to20MPa. Simulation result is shown in Figs. 5 and 6.Prightis adjusted to 20MPa as the step signal is given.There is a small overshoot of the pressure in Fig. 5 as thereis a mass-spring system in the pilot stage. Overshoot of theFig. 3Simulation model of the thrust systemFig. 4Thrust force versus advancing speed in soft ground 4Table 1Main simulation parametersItemSetting valuePump maximum displacement30cc/revRelief pressure35.3MPaNominal pump speed1500revPiston diameter of cylinder600mmRod diameter of cylinder480mmForce exerted on cutter head3200kNFriction force6000kNZhibin LIU et al. Simulation analysis of pressure regulation of hydraulic thrust system379mass-spring system causes overshoot of the outlet pressurein the main stage. Plefthas a pulse when Prightis adjustedand increases slightly after adjustment. The sudden changein inlet pressurewill causethesame pulseinoutletpressureat first.Because the pilot stage frequency response is not highenough, when the pilot stage mechanism starts adjustingthe valves opening area, outlet pressure will decrease tothe set value. The small increase of Pleftmight be caused bythe increase of pump outlet flow rate. The pump outlet flowrate will be discussed next. This small difference inpressure will not affect the tunnel excavation. Higheradvancing speed is achieved on the right side, as shown inFig. 6. A left steering motion is carried out.4.2Pump displacement adjustmentPump displacement should be adjusted when pressureregulation is carried out. Three cases are illuminated toexplain the problem. Pressure regulation is operated as inthe previous case.Case 1: Displacement maintains at about 75% ofmaximum. The result is shown in Fig. 7.Prightis adjusted to 20MPa. Pressure regulation isachieved. However, pump outlet pressure is at 35.3MPa,which means the system is overloaded and the pressurerelief valve opens. Power loss caused by relief flow isconsiderable.Case 2: Displacement maintains at about 50% ofmaximum. The result is shown in Fig. 8.Pumpoutlet pressure issensitivetotheloadpressure.Thereis no overload during pressure regulation. However, thrustpressure cannot be adjusted to 20MPa because oil flowsupply is not enough. Higher thrust pressure causes higheradvancing speed, which means the cylinder requires more oilflow rate. Pressure regulation is invalidated in this case.Case 3: Displacement is set at 50% at first, then 75%when pressure regulationis carried out. The result is shownin Fig. 9.There is no overload. Pump outlet pressure is sensitiveto the load pressure. Thrust pressure can be adjusted to20MPa. This is because pump displacement is adaptive tothe system. A pressure regulation should be together with apump displacement regulation.4.3A tough situationIn practice, an optimal tunnel project is worked out afterconsidering commuters needs, commercial demand,geological conditions, and so on. Shield tunneling machineis expected to advance in good geological conditions.Normally, a geological survey is done before the excava-tion process. It is impossible, however, to know everythingFig. 5Pressures of right and left cylinders during pressureregulation of left steeringFig. 6Displacements of right and left cylinders during pressureregulation of left steeringFig. 7Pressures of pump outlet and right cylinder when pumpdisplacement maintains at 75% of maximum displacement380Front. Mech. Eng. 2011, 6(3): 377382in the path of the machine. Unexpected conditions such ashard rock, wooden poles, quicksand or underground rivermay present themselves. In this study, we simulate such anexacting case, with the machine encountering some hardstratum on the right side. The following shows how thepressure regulation works and how the machine behaves.The simulation result is shown in Figs. 10 and 11.Note: Time domain is used as x-axis in the simulation.However, time is not practical data. Time setting isartificial for the purpose of the illustration. Time periodmay be much longer in a real-world tunnelling process.05s: The machine is advancing straight in soft soil atnormal speed. Thrust pressure is 14MPa.515s: The machine is advancing from soft soil into hardsoil on the right side. Right cylinder speed (Vright) decreasesbecause Prightis not enough to maintain the normal speed.This causes surplus pump outlet flow rate and increase insystem pressure. Pleftand left cylinder speed (Vleft) increase.System pressure increases until relief valve is open.Meanwhile, Pleftand Vleftdrop to normal levels.At 20s: Prightis adjusted to 31MPa. A pulse occurs inPleftand causes a pulse in Vleft, as described before.Because an increase of flow rate occurs in right cylinder,flow rate of relief valve will decrease suddenly, causing asudden drop in system pressure.At 25s: Vleftshould decrease to ensure straight advance.However, as Vleftis higher than Vright, an unwanted rightsteering motion is carried out. Manual control is applied todecrease Pleftuntil the machine advances straight.At 30s: Pump displacement is adjusted. After pressureregulation, the machine is now advancing at a lower speed.Pump displacement should decrease until overload isavoided, as over-adjustment will cause decrease of thrustpressure and advancing speed.Fig. 8Pressures of pump outlet and right cylinder when pumpdisplacement maintains at 50% of maximum displacementFig. 9Pressures of pump outlet and right cylinder when pumpdisplacement is adjusted from 50% to 75% of maximumdisplacement when pressure regulation is appliedFig. 10Pressures of pump outlet, right cylinder, and left cylinderas the machine advances into and then out of some hard soilFig. 11Velocities of right cylinder and left cylinder as themachine advances into and then out of some hard soilZhibin LIU et al. Simulation analysis of pressure regulation of hydraulic thrust system3814050s: The machine is advancing out of the hard soil.Prightdecreases as the machine goes into soft soil little bylittle. Prightis rather high at the beginning, which causesspeed increases. Oil supply is not enough for the systemanymore as Vrightincreases. This causes a drop in systempressure, and Prightdecreases.At 55s: Thrust pressure is adjusted. Thrust pressure maybe set to 14MPa. Pressure regulation should take placebefore pump displacement adjustment. A slight increase ofthrust speed happens due to the increase in thrust pressure.Oil supply is not enough, however, and pressure regulationis invalidated.At 60s: Pump displacement is adjusted. As pumpdisplacement increases, thrust pressure is adjusted to14 MPa and thrust speed increases. The machine isadvancing at normal speed from now on. Of course,there is a little angle change of advancing orientationcompared to the initial angle. The simulation is to showhow the system behaves during the whole adjustment. Ifangle control is critical, angle feedback and steeringcontrol can be applied.Adjustment usually takes place shortly after desynchro-nization. But in the simulation, adjustment takes placewhen the machine is “totally” advancing into hard stratum.The purpose is to find out what happens during the wholeencounter, in other words, to find out the potential problemof the system.5ConclusionsPressure regulation of the thrust system on a shieldtunneling machine is studied in this paper. Pressureregulation includes two parts: pressure setting of thrustcylinders, and pump displacement adjustment.1) Pressure regulation of one cylinder group mayinfluence the pressures of the other groups. Increasing acertain groups pressure and pump outlet flow rate maycause small pressure increases in other groups. This smallchange in pressure is acceptable in tunnel excavation.2) Pump displacement adjustment should be carried outwhen pressure regulation is applied. If pump outlet flowrate is more than the system demand, pressure regulationwill also be achieved albeit with an unwanted pumppressure overload. If pump outlet flow rate is less than thesyste

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