Unit-18-Fluid-and-Hydraulic-System-机电专业英语-图文课件

1、Unit 18 Fluid and Hydraulic SystemContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions hydraulic system 液压系统prehistoric pri:histrik adj. 史前的，很久以前的harness h:nis v. 利用(风等)作动力，治理，控制watermill w:tmil n. 水车，水磨hydraulic motor 液压电动机mosaic mzeiik

2、n. 镶嵌细工，马赛克domestication dmestikein n. 家养，驯养displacement displeismnt n. 位移，转移，置换New Words & Expressions layer lei n. 层，层次tangential tndenl adj. 切线的，切向的Newtonian njutnin adj. 牛顿的，牛顿学说的nonlinear nnlini adj. 非线性的，非直线的rotational ruteinl adj. 旋转的，转动的，循环的compressible kmpresibl adj. 可压缩的，可压榨的Pascals law 帕斯

3、卡定律pressurize preraiz v. 增压，给加压New Words & Expressions intake inteik n. 入口，进口，进入量tank tk n. 油箱，水箱，池塘.reservoir rezvw: n. 蓄水池，水箱，蓄能器atmospheric tmsferik adj. 大气的，空气的discharge dist:d n. 卸货，出料，流出; vi. 卸下，放出preference prefrns n. 优先选择compact kmpkt adj. 紧凑的，紧密的，简洁的New Words & Expressions diagrammatic daig

4、rmtik adj. 图表的，概略的oil pressure pump 液压泵hydraulic cylinder 液压缸kinetic energy 动能hydrostatic driver 静压传动variable-delivery pump 变量泵by no means 决不self-contained adj. 独立的，配套的，整体的New Words & Expressions stimulate stimjuleit v. 促进，激励hydraulics haidr:liks n. 水力学，液压系统resilience rizilins n. 跳回，恢复力，回弹virtue v:t

5、u: n. 优点，效力，功能detriment detrimnt n. 损害，不利regrind ri:graind v. 重磨Text & TranslationHydraulic power has a long history，which dates from mans prehistoric efforts to harness the energy in the world around him. The only sources readily available were the water and the windtwo free and moving streams. The

6、 watermill，the first hydraulic motor，was an early invention. One is pictured on a mosaic at the Great Palace in Byzantium，dating from the early fifth century. The Romans had built the mill. But the first record of a watermill dates back even further，to around 100 BC，and the origins may indeed have b

7、een much earlier. Text & TranslationThe domestication of grain began some 5 000 years before and some enterprising farmers may have become tired of pounding or grinding the grain by hand. Perhaps，in fact，the inventors were some farmers wives. Since they often drew the heavy jobs. Fluid is a flowing

8、substance；that is，its constituent particles may continuously change their positions relative to one another. Moreover，it offers no lasting resistance to the displacement，however great，of one layer over another. This means that，if the fluid is at rest，no shear force (that is a force tangential to the

9、 surface on which it acts) can exist in it. Text & TranslationFluid may be classified as Newtonian and non-Newtonian. 1In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. In non-Newtonian fluid there is a nonlin

10、ear relation between the magnitude of applied shear stress and the rate of angular deformation. The flow of fluids may be classified in many ways，such as steady or non-steady，rotational or irrotational，compressible or incompressible，and viscous or no viscous. Text & Translation2All hydraulic systems

11、 depend on Pascals law，named after Braise Pascal，who discovered the law. This law states that pressurized fluid within a closed containersuch as cylinder or pipeexerts equal force on all of the surfaces of the container. In actual hydraulic systems，Pascals law defines the basis of the results which

12、are obtained from the system. Thus，the liquid is moved by a pump in the system. The intake of the pump is connected to a liquid source，usually called the tank or reservoir. Atmospheric pressure，pressing on the liquid in the reservoir，forces the liquid into the pump. When the pump operates，it forces

13、liquid from the tank into the discharge pipe at a proper pressure. Text & TranslationThe flow of the pressurized liquid discharged by the pump is controlled by valves. Three control functions are used in most hydraulic systems：control of the liquid pressure，control of the liquid flow rate，and contro

14、l of the direction of flow of the liquid. Hydraulic drives are used in preference to mechanical systems when power is to be transmitted between point too far apart for chains or belts；high torque at low speed is required；a very compact unit is needed；a smooth transmission，free of vibration，is requir

15、ed；easy control of speed and direction is necessary；and output speed is varied steplessly. Text & TranslationFig.18.1 gives a diagrammatic presentation of the components of a hydraulic installation. 3Electrically driven oil pressure pumps establish an oil flow for energy transmission，which is fed to

16、 hydraulic motors or hydraulic cylinders，converting it into mechanical energy. The control of the oil flow is by means of valves. The pressurized oil flow produces linear or rotary mechanical motion. The kinetic energy of the oil flow is comparatively low，and therefore the term hydrostatic driver is

17、 sometimes used. There is little difference in construction between hydraulic motors and pumps. Any pump may be used as a motor. The quantity of oil flowing at any given time may be various by means of regulating valves (as shown in Fig.181) or the use of variable delivery pumps. Text & TranslationF

18、ig. 18-1 Speed-control Methods for Hydraulic Motors Text & TranslationThe application of hydraulic power to the operation of machine tools is by no means new，though its adoption on such a wide scale as exists at present is comparatively recent. It was in fact the development of the modern self conta

19、ined pump unit that stimulated the growth of this form of machine tool operation. Hydraulic machine tool drive has a great number of advantages. One of them is that it can give infinitely variable speed control over wide ranges. In addition，they can change the direction of drive as easily as they ca

20、n vary the speed. As in many other types of machine，many complex mechanical linkages can be simplified or even wholly eliminated by the use of hydraulics. Text & TranslationThe flexibility and resilience of hydraulic power is another great virtue of this form of drive. Besides the smoothness of oper

21、ation thus obtained，a great improvement is usually found in the surface finish on the work and the tool can make heavier cuts without detriment and will last considerably longer without regrinding.Text & Translation水力的历史由来已久，始于人类为利用它周围的能源而做出的努力。容易利用的能源就是水和风两种自由的流动流体。第一台液力装置水车是最早的发明。从5世纪早期，水车图画就出现在大宫

22、殿的马赛克上。磨粉机由罗马人发明，而水磨机的历史更早，可以追溯到大约公元前100 年。当一些上进的农场主厌恶由手工冲击、研磨谷物时，谷物的家庭养殖已开始5000 多年。也许，真正的发明家是那些农场主的妻子，因为她们经常要干重的农活。Text & Translation流体是可以流动的物体，也就是说，构成物质的粒子可以连续地改变它们之间的相对位置，而且，它提供流体层间流动非连续的阻力。这意味着流体在静止时，在其内部没有剪切力(作用表面切向方向的受力)存在。流体可以分为牛顿流体或非牛顿流体。在牛顿流体中，流体层间作用的剪切力和角度变形总量的大小成线性关系。在非牛顿流体中，流体层间作用的剪切力和角度

23、变形总量的大小成非线性关系。Text & Translation流体的流动可按多种方式分类，如定常流或非定常流、有旋流或无旋流、可压缩流或不可压缩流以及黏性流或无黏性流。所有的液压系统遵循于帕斯卡定律，命名是由Braise Pascal 而来的，是他发明了此定律。这条定律指出在密封容积内压缩的液体例如圆柱筒或管子在容积的各个不同面上作用着相等的力。Text & Translation在实际液压系统中，帕斯卡定律是解释从系统中获得的各种结果的基础。因此，泵使液体在系统中流动，泵的进口连接液流源，通常叫油槽或油箱。作用在油箱液面上的气压使流体进入油泵。当油泵工作时，在适当的压力作用下，油泵迫使流体

24、从油箱流动到出口。由油泵泵出的压缩液体通过各种阀门来控制。在大多数液压系统中采用3种控制功能：(1) 液体压力的控制；(2) 液体流速的控制；(3) 液体流动方向的控制。Text & Translation当处于下列几种情况时，液压驱动被优先使用。：(1) 对于链传动和皮带传动来说，功率的传递位置太远。(2) 低速高转矩的场合。(3) 很紧凑的结构。(4) 要求传动平稳、避免振动的场合。(5) 速度和方向容易调节的场合。(6) 输出速度无级可调的情况。Text & Translation如图18-1 所示给出了液压元件安装的图形布局。由电气驱动的油泵供有传递能量用的油量，并可传递给液压电动机或

25、油缸，从而将液压能转换成机械能。通过阀门控制油的流动，压力油流产生线性的或旋转的机械运动。油流的动能相对比较低，因此有时采用静压传动。液压电动机和液压油缸之间几乎不存在构造上的不同。任一油泵可以被用作液压电动机。在任一时间里的油流量可以通过调节阀门(如图18-1所示)或采用变量泵来改变。Text & Translation图18-1 液压电动机的速度控制方法Text & Translation液压传动运用到机床的运行中绝不是新的，虽说现在的大规模采用出现不久。现代油泵的发展促进了这类机床运行的增多。机床的液压驱动具有许多优点。其中一个是液压驱动在广泛的范围内提供无限变化的速度。另外，它们能像改

26、变速度一样容易来改变驱动的方向。像许多其他类型的机床一样，许多复杂的机械装置能够被简单化或者由于液压驱动的使用完全取消。液压驱动的另一个优点是它的柔性和缓冲性。除了运行平稳外，还发现了许多改进，如工件表面光洁度的改善，在不损坏刀具的前提下能加大刀具的负荷，并能在刃磨刀具的情况下工作更长时间。Complex Sentence Analysis1 Hydraulic power has a long history, which dates from mans prehistoric efforts to harness the energy in the world around him. 水力

27、的历史由来已久，始于人类为利用其周围的能源而做出的努力。 date from： 从什么时候开始 prehistoric efforts：很久以前的努力Complex Sentence Analysis2 In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. 在牛顿流体中，流体层间作用的剪切力和角度变形总量的大小成线性关系。applied shear stresses：作

28、用的剪切应力 the resulting rate：总的合率(量) Complex Sentence Analysis3 All hydraulic systems depend on Pascals law, named after Braise Pascal, who discovered the law. 所有的液压系统遵循于帕斯卡定律，命名是由Braise Pascal 而来的，是他发明了此定律。 depend on：遵循于 named after：根据命名的,此句是过去分词短语做定语修饰 Pascals law。 who discovered the law 是非限定性定语从句，修饰Braise Pascal Complex Sentence Analysis4 Electrically driven oil pressure pumps establish an oil flow for energy transmission, which is fed to hydraulic motors or hydraulic cylinders, converting it into mechanical energy. 由电气驱动的液压泵供有传递能量用的油量，并可传递给液压电动机或液压缸，从而将液压能转换成机械能。 which is fed t