液压传动试题12A1-答案及评分标准.pdf

四四 川川 大大 学学 期期末末 考考 试试 试试 题题 2012 2013学年第上学期 课程号 302155020 课序号 课程名称 液气压传动及控制 任课教师 熊瑞平 傅波 刘苏 成绩 适用专业年级 10 级机制专业学生人数 400印题份数 学号 姓名 考考考考 试试试试 须须须须 知知知知 四川大学学生参加由学校组织或由学校承办的各级各类考试 必须严格执行 四川大学考试工四川大学学生参加由学校组织或由学校承办的各级各类考试 必须严格执行 四川大学考试工 作管理办法作管理办法 和和 四川大学考场规则四川大学考场规则 有考试违纪作弊行为的有考试违纪作弊行为的 一律按照一律按照 四川大学学生考试违纪四川大学学生考试违纪 作弊处罚条例 进行处理 作弊处罚条例 进行处理 四川大学各级各类考试的监考人员 必须严格执行 四川大学考试工作管理办法四川大学各级各类考试的监考人员 必须严格执行 四川大学考试工作管理办法 四川大学 四川大学 考场规则考场规则 和和 四川大学监考人员职责四川大学监考人员职责 有违反学校有关规定的有违反学校有关规定的 严格按照严格按照 四川大学教学事故认四川大学教学事故认 定及处理办法 进行处理 定及处理办法 进行处理 TestTestTestTest ofofofof FluidFluidFluidFluid PowerPowerPowerPower andandandandApplicationsApplicationsApplicationsApplications A A A A No No No No 1 1 1 12 2 2 23 3 3 34 4 4 45 5 5 56 6 6 6TotalTotalTotalTotal ScoreScoreScoreScore 1 1 1 1 FillFillFillFill outoutoutout thethethethe blanks blanks blanks blanks 2 2 2 25 5 5 5 1 Fluid power is the technology which deals with the generation control and transmission of power using 压缩流体 2 泵 which is the heart of a hydraulic system converts mechanical energy into pressure energy 3 If the absolute pressure is 80 bar at the outlet of a pump the gauge pressure is 7 9 MPa respectively If the absolute pressure at the inlet to the pump is 0 08 MPa the suction vacuum pressure is 0 2 bar Assume that the atmosphere pressure is 0 1 MPa 4 Fluid power can be transmitted through either linear or rotary motion by using linear actuators called 液压缸 油缸 or rotary actuators called 马达 5 Generally the design of the internal gear pump consists of an 内齿轮 a regular spur gear 月 牙型密封块 and an external housing 6 There are two basic types of piston pumps One is 轴向式 The second type is 径向式 7 Generally speaking a fluid should be changed when its 粘度 and 酸性 increase due to fluid breakdown or contamination 8 Piston motors generate torque by pressure acting on the ends of 柱 塞 reciprocating inside a cylinder block 9 Essentially a hydraulic fluid has four primary functions to传递功率 to lubricate moving parts to密封两部件间的间隙 and to dissipate heat 注 1 试题字迹务必清晰 书写工整 本题4页 本页为第 1页 2 题间不留空 一般应题卷分开 教务处试题编号 3 务必用 A5 纸打印 学号 姓名 10 A gear pump has a 7 6 cm outside diameter a 5 1 cm inside diameter and a 2 5 cm width If the actual pump flow at 1800rpm and rated pressure is 106 L min the volumetric efficiency is 94 5 3 11 The electrohydraulic stepper motor consists of three components electrical stepper motor 液压伺服 阀 and hydraulic motor 12 A system consisting of a 液压泵 a hydraulic motor and 阀 and pipes can be used to provide adjustable speed for many practical applications Such a system is called hydraulic transmission system 13 Ahydraulic cylinder has a volume of 60L at the atmospheric pressure as the pressure increases the volume decreases to 59 9L the rising value of the pressure is 1 17MPa The hydraulic oil bulk modulus is 7000 105Pa 2 14 The kinematic viscosity of a hydraulic oil is 100 cSt If the fluid is flowing in a 3 mm diameter pipes at a velocity of 10 mm s the Reynolds number is0 3 2 2 2 2 2 ChooseChooseChooseChoose thethethethe bestbestbestbest answeransweransweranswer forforforfor eacheacheacheach question question question question 2 2 2 20 0 0 0 1 If the Reynolds number of a hydraulic oil flowing in a pipe is 5000 the flow isA A turbulentB laminarC neither turbulent nor laminarD transition region 2 For a compound relief valve after the main valve has relieved the system and when pressure is smaller than the setting of valve what does pilot valve do B A It remains open until after the main valve closes B It closes simultaneously the main valve C It closes first and allows pressure to equalize above and below the main piston D It closes first and causes pressure above the main piston to force the main valve closed 3 Which of the following spring centered flow paths for three position four ways valves can lock actuators and unload the pump D A type P B type O C type Y D type M 4 Fig 1 illustrates the operation of external gear pump The oil ports marked with A are discharge port A a and c B b and dC a and b D c and d ab cd FigureFigureFigureFigure 1 1 1 1 P A B C Q FigureFigureFigureFigure 2 2 2 2FigureFigureFigureFigure 3 3 3 3 Fig 1Fig 2 5 For the pressure control circuit in Fig 2 if A 2 stage pressure control can be accomplished A p1 p2B p1 p2C p1 p2D p1 p2 P A B C Q FigFigFigFig 3 3 3 3 本题4页 本页为第 2 页 教务处试题编号 学号 姓名 6 Fig 3 shows pressure versus flow rate curve for pressure compensated vane pump When we adjust A the slop of BC line will change A the stiffness of compensator spring B the pressure compensator C the initial eccentricityD swash plate angle 7 Which of the following leakage losses does affect the volumetric efficiency of vane pumps D A Leakage around the outer periphery of the gears B Leakage across the faces of the gears C Leakage at the points where the gear teeth make contact D Leakage across the faces of the rotor and between the wear plates and the pressure ring 8 A vane motor develops torque by the hydraulic pressure acting on the exposed surfaces of the C A Cam ringB Gear teethC VanesD Rotor 9 For a double acting cylinder hooked up in the regenerative circuit 差动回路 ifthe extending speed of the hydraulic cylinderisthethree timestheretractingspeed the ratioofthe piston diameter and the rod diameter is B A 1B 2C 3D 4 10 The pressure compensated flow control valve speed regulating valve is composed by a B and a throttle valve that are mounted in series A Pressure relief valveB Pressure reducing valveC Directional valveD Safe valve 3 3 3 3 TrueTrueTrueTrue orororor falsefalsefalsefalse 2 2 2 22 2 2 2 1 Pumps do not pump pressure Instead they produce fluid flow The resistance to this flow is what determines the pressure T 2 Ifthe viscosity is too low the result is increased pressure drop through valves and lines F 3 An oil having low viscosity index is one that exhibits a large change in viscosity with temperature change T 4 Speed and torque depend on the swash plate angle of thein line piston motor The smaller the angle the greater the displacement and torque but the smaller the speed F 5 One disadvantage of a balanced vane pump is that is cannot be designed as a variable displacement unit T 6 All pumps operate on the principle whereby a partial vacuum is created at the pump outlet due to the internal operation of the pump F 7 Liquids rather than gases are used in hydraulic systems because liquids are more compressible F 8 Bourdon gauges can be used to measure hydraulic pressure T 9 The conservation of energy law states that energy can neither be created nor destroyed F 10 The purpose of a pressure reducing valve in hydraulic circuit is usually to maintain control of a vertical cylinder to prevent is from descending due to gravity F 11 In a closed circuit drive exhaust oil from the motor is returned directly to the pump inlet T 4 4 4 4 A A A Aspeedspeedspeedspeed reducerreducerreducerreducer requiresrequiresrequiresrequires thethethethe hydraulichydraulichydraulichydraulic motormotormotormotor totototo putputputput outoutoutout a a a a torquetorquetorquetorque ofofofof 52 552 552 552 5 N N N N mmmm andandandand a a a a rotatingrotatingrotatingrotating speedspeedspeedspeed ofofofof 30r min 30r min 30r min 30r min TheTheTheThe hydraulichydraulichydraulichydraulic motormotormotormotor deliverdeliverdeliverdeliver is is is is 12 5cm12 5cm12 5cm12 5cm3 3 3 3 r r r r andandandand bothbothbothboth thethethethe volumetricvolumetricvolumetricvolumetric andandandand mechanicalmechanicalmechanicalmechanical efficienciesefficienciesefficienciesefficiencies ofofofof thethethethe hydraulichydraulichydraulichydraulic motormotormotormotor areareareare 0 9 0 9 0 9 0 9 WhatWhatWhatWhat areareareare thethethethe practicalpracticalpracticalpractical volumetricvolumetricvolumetricvolumetric flowflowflowflow raterateraterate andandandand thethethethe pressurepressurepressurepressure needed needed needed needed 8 8 8 8 本题4页 本页为第 3 页 教务处试题编号 学号 姓名 解 解 min 7 416min 7 416 9 0 min 30 5 12 3 3 mLcm rrcmnq Q v v 4 4 4 4 分分 MPa rcm Nm q T p mv 3 29 9 0 5 12 2 5 522 3 4 4 4 4 分分 5 5 5 5 TheTheTheThe VenturiVenturiVenturiVenturi metermetermetermeter reducesreducesreducesreduces thethethethe pipepipepipepipe diameterdiameterdiameterdiameter fromfromfromfrom 0 1m0 1m0 1m0 1m totototo a a a a minimumminimumminimumminimum ofofofof 0 05m0 05m0 05m0 05m asasasas shownshownshownshown inininin Fig Fig Fig Fig 4 4 4 4 CalculateCalculateCalculateCalculate thethethethe volumetricvolumetricvolumetricvolumetric flowflowflowflow raterateraterate andandandand thethethethe massmassmassmass flowflowflowflow raterateraterate assumingassumingassumingassuming idealidealidealideal conditions conditions conditions conditions thethethethe densitydensitydensitydensity ofofofof waterwaterwaterwateris is is is 1 1 1 1x10 x10 x10 x103 3 3 3kg mkg mkg mkg m3 3 3 3 thethethethe densitydensitydensitydensity ofofofof HgHgHgHg is is is is 13 613 613 613 6x10 x10 x10 x103 3 3 3kg mkg mkg mkg m3 3 3 3 1 1 1 10 0 0 0 Fig 4 解 由水银压力计可知 ba pp 即2 1 6 13 2 1 21 ggzpzgp 水水水 2 分 其中 z 为水银柱的顶部到管子中心线的距离 则由该压力计得出 m g pp 12 15 21 水 由流量连续性有 2211 AvAv 2 分 11 2 1 2 4vv A A v 根据理想条件下的伯努利方程 g v g p z g v g p z 22 2 22 2 2 11 1 水水 2 分 0 2 2 2 2 121 g vv g pp 水 0 2 16 12 15 2 1 2 1 g vv smv 45 4 1 因此 体积流量为 因此 体积流量为 min 2100 035 0 5 405 0 332 11 LsmsmvAqv 2 2 2 2 分分 质量流量为 质量流量为 skgskgqq vm 35 035 0 1000 水 2 2 2 2 分分 6 6 6 6 AsAsAsAs is is is is shownshownshownshown inininin Fig 5Fig 5Fig 5Fig 5 thethethethe effectiveeffectiveeffectiveeffective workingworkingworkingworking areasareasareasareas ofofofof thethethethe hydraulichydraulichydraulichydraulic cylinderscylinderscylinderscylinders A A A A11111111 A A A A21212121 100cm 100cm 100cm 100cm2 2 2 2 A A A A12121212 A A A A22222222 50cm 50cm 50cm 50cm2 2 2 2 TheTheTheThe workingworkingworkingworking loadsloadsloadsloads ofofofof twotwotwotwo cylinders cylinders cylinders cylinders F F F FL1L1L1 L1 35000N 35000N 35000N 35000N F F F FL2 L2L2L2 25000N 25000N 25000N 25000N thethethethe settingsettingsettingsetting pressurespressurespressurespressures ofofofof thethethethevalvevalvevalvevalve valvevalvevalvevalve andandandand valvevalvevalvevalve areareareare 5MPa 5MPa 5MPa 5MPa 4MPa4MPa4MPa4MPa andandandand 3MPa3MPa3MPa3MPa respectively respectively respectively respectively If If If If frictionfrictionfrictionfriction resistance resistance resistance resistance inertialinertialinertialinertial force force force force thethethethe pressurepressurepressurepressure losslosslossloss inininin pipelinespipelinespipelinespipelines andandandand directionaldirectionaldirectionaldirectional controlcontrolcontrolcontrol valvevalvevalvevalve areareareare neglected neglected neglected neglected 15 15 15 15 1 1 1 1 WWWWhathathathat areareareare thethethethe pressurespressurespressurespressures P P P PA A A A P P P PB B B B P P P PC C C Cunderunderunderunder thethethethe workingworkingworkingworking conditionsconditionsconditionsconditions ofofofofA A A A B B B B C C C C A A A A TheTheTheThe hydraulichydraulichydraulichydraulic pumppumppumppump startsstartsstartsstarts andandandand thethethethe twotwotwotwo directionaldirectionaldirectionaldirectional controlcontrolcontrolcontrol valvesvalvesvalvesvalves areareareare atatatat middlemiddlemiddlemiddle positions positions positions positions B B B B SolenoidSolenoidSolenoidSolenoid2YA2YA2YA2YAis is is is actuatedactuatedactuatedactuated andandandand cylindercylindercylindercylinder II II II II movmovmovmoveseseses forwardsforwardsforwardsforwards atatatat workingworkingworkingworking feedfeedfeedfeed speed speed speed speed C C C C SolenoidSolenoidSolenoidSolenoid2YA2YA2YA2YAis is is is releasedreleasedreleasedreleased andandandand1YA1YA1YA1YAis is is is actuated actuated actuated actuated cylindercylindercylindercylinder I I I I movmovmovmoveseseses forwardsforwardsforwardsforwards atatatat workingworkingworking