液气压传动 第一章 概述.ppt

1、液气压传动及控制Fluid Power with Applications,刘 甦,第一章 概述（Introduction） 1.1 什么是流体传动？（WHAT IS FLUID POWER?） 1.流体传动与控制（Fluid power and control） 流体传动是一门利用有压力的流体实现动力的产生、控制和传输的技术。可以这么说流体传动是运动机器的动力。这是因为流体传动被用来实现现代工业所有机器的推、拉、调节或驱动（Fluid power is the technology which deals with generation, control, and transmission

2、of power using pressurized fluids. It can be said that fluid power is the muscle that moves industry. This is because fluid power is used to push, pull，regulate, or drive virtually all the machines of modern industry.）。例如：流体传动操纵和制动汽车、发射宇宙飞船、运输,土方、收割庄稼、采煤、驱动机床、操纵飞机、加工食品、甚至于钻牙等。事实上， 在产品的加工或销售过程的某些环节离开

3、了流体传动与控制几乎是不可能实现的（For example, fluid power steers and brakes automobiles, launches spacecrafts, moves earth, harvests crops, mines coal, drives machine tools, controls airplanes, processes food, and even drills teeth. In fact, it is almost impossible to find a manufactured product which hasnt been “

4、fluid-powered” in some way at some stage of its production or distribution.）。,2.流体传动的介质（Fluid power medium） 鉴于流体既可以是液体也可以是气体，流体传动与控制包含液压传动和气压传动。液压系统使用像石油基润滑油、水、合成油甚至金属溶液这样的液体。气压传动以空气作为传动介质，因为空气非常丰富并且在完成指定的工作后容易排入大气（Since a fluid can be either a liquid or a gas, fluid power is actually the general te

5、rm used for hydraulics and pneumatics. Hydraulic systems use liquids such as petroleum oils, water, synthetic oils, and even molten metals. Pneumatic systems use air as the gas medium because air is very abundant and can be readily exhausted into the atmosphere after completing its assigned task）。 3

6、.流体系统的类型（Types of fluid systems） 认识到，实际上有两种不同类型的流体系统：流体,输送和流体传动。（It should be realized that there are actually two different types of fluid systems: fluid transport and fluid power）。 流体输送系统（Fluid transport systems）：其唯一目的是将流体从某个地方输送到另一地方以满足某些用途。例子包括抽水站抽水到家，跨国的天然气管道，化学处理系统中的各种流体汇集。（Fluid transport sys

7、tems have as their sole objective the delivery of a fluid from one location to another to accomplish some useful purpose. Examples include pumping stations for pumping water to homes, cross-country gas lines, and systems where chemical processing takes place as various fluids are brought together.）。

8、 流体传动与控制系统（Fluid power and control systems）：为完成工作而专门设计的。这个工作是由,直接承受压力流体的工作缸或流体（液压）马达来完成的，依次为希望的动作提供动力。当然，需要控制元件以确保工作平稳、准确、高效、安全地完成（Fluid power systems are designed specifically to perform work. The work is accomplished by pressurized fluid bearing directly on an operating cylinder or fluid motor, wh

9、ich, in turn, provides the muscle to do the desired work. Of course, control components are also needed to ensure that the work is done smoothly, accurately, efficiently, and safely）。,4.流体传动与控制的应用范围（Fluid power and control application range） 功率（Power）：操作员轻触按钮就能控制数百马力的功率并通过管路将其传递到任何位置（A feather touch

10、 by an operator can control hundreds of horsepower and transmit it to any location where a hose or pipe can go）。 精密度（Precision）：像在机床工业中的应用，能够重复达到万分之一英寸的公差（In terms of precision such as applications in the machine tool industry, tolerances of one ten-thousandth of an inch can be achieved and repeated

11、 over again）。 流体传动与控制不仅仅是动力的源泉，它同时对完成所需的工作提供平稳、高效、安全和准确并可控、可变的动力（Fluid power is not merely a powerful muscle;,it is a controlled，flexible muscle which provides power smoothly, efficiently, safely, and precisely to accomplish useful work）。,1.2 流体传动的优点（ADVANTAGES OF FLUID POWER） 现在有三种基本的传动方式：电力、机械和流体传

12、动。在大多数实际应用中，都是这三种方法进行组合以使整个系统的效率最高。掌握每一类型的特点对正确决定使用哪种方法是很重要的。例如：流体传动系统能够比机械传动更经济地远程传输动力。但是, 与电力系统相比流体传动系统传输距离受到限制（There are only three basic methods of transmitting power: electrical, mechanical, and fluid power. Most applications actually use a combination of the three methods to obtain the most ef

13、ficient overall system. To properly determine which principle method to use, it is important to know the salient features of each type. For example, fluid systems can transmit power more economically over,greater distances than can mechanical types. However, fluid systems are restricted to shorter d

14、istances than are electrical systems）。 流体传动成功和广泛应用的奥秘是它的变化多端和控制容易。流体传动不受通常的机械系统中机器的几何关系阻碍。并且，功率能够几乎无限量的传递因为与电力系统相比流体传动系统不受材料自身的物理性能的限制。例如：电磁铁的特性受到钢材的磁性饱和的限制。另一方面，流体传动系统的功率仅受材料强度大小的限制（The secret of fluid powers success and widespread use is its versatility and manageability. Fluid power is not hinder

15、ed by the geometry of the machine as is the case in mechanical systems. Also, power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of,materials as are the electrical systems. For example, the performance of an electromagnet is l

16、imited by the saturation limit of steel. On the other hand, the power limit of fluid systems is limited only by the strength capacity of the material）。 为了提高生产率工业生产越来越依赖工业自动化。这包含了对生产操作，制造过程和材料输送的远程和直接控制。流体传动因以下四个突出优点在工业自动化中发挥着重要的作用（Industry is going to depend more and more on automation in order to i

17、ncrease productivity. This includes remote and direct control of production operations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories.）。,1.控制简单和精确（Ease and accuracy of control） 借助于简单的杆件和按钮的使用，流体传动

18、系统的操作人员很容易进行开始、停止、加速和减速操作，并且对于提供的任何所需功率其位置精度都可达到十万分之一英寸（By the use of simple levers and push buttons, the operator of a fluid power system can readily start, stop, speed up or slow down, and position forces which provide any desired horsepower with tolerances as precise as one ten-thousandth of an i

19、nch）。 2.力的放大（Multiplication of force） 一个液压系统（不使用笨重的齿轮、皮带轮和操纵杆）能简单而有效地将力从几分之一盎司放大到数百吨对外输出（A fluid power systems （without using cumbersome gears, pulleys, and levers）can multiply forces simply and efficiently from a fraction of an ounce,to several hundred tons of output）。 3.恒定的力或转矩（Constant force or t

20、orque） 只有流体传动系统能够提供不受速度变化影响的恒定力或转矩。不论工作速度是每小时几英寸还是每分钟几百英寸，每小时几转还是每分钟上千转，力或转矩都能保持恒定（Only fluid power systems are capable of providing constant force or torque regardless of speed changes. This is accomplished whether the work output moves a few inches per hour, several hundred inches per minute, a fe

21、w revolutions per hour, or thousands of revolutions per minute）。 4.简便、安全、经济（Simplicity, safety, economy） 流体传动系统与机械或电力系统相比仅使用少量的运动部件。所以，操作和维修保养更加简便。其次，安全性高，体积小和可靠性好（In general fluid power,systems use fewer moving parts than comparable mechanical or electrical systems. Thus，they are simpler to maintai

22、n and operate. This, in turn maximizes safety, compactness, and reliability）。 流体传动系统另外的优点包括即时的反向运动，自动过载保护和无级调速。在任何已知的动力源中流体传动系统具有最高的功率重量比（Additional benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Flu

23、id power systems also have the highest horsepower per weight ratio of any known power source）。 尽管液压传动有这些优点，它也不是所有动力传递问题的灵丹妙药。液压系统总有一些缺点。液压油是肮脏的，并且泄漏是不可能完全避免的。如果设计错误，,液压管道可能破裂，飞散的物体能够导致人身伤害。此外，如果液压油泄漏进高温设备中，很多液压油能够引起火灾。因此，为了确定最好的总体设计每一种使用状况都必须被彻底地研究（In spite of all these highly desirable features of

24、fluid power, it is not a panacea for all power transmission problems. Hydraulic systems also have some drawbacks. Hydraulic oils are messy, and leakage is impossible to completely eliminate. Hydraulic lines can burst, possibly resulting in human injury due to flying objects, if proper design is not

25、implemented. Also, most hydraulic oils can cause fires if an oil leak occurs in an area of hot equipment. Therefore, each application must be studied thoroughly to determine the best overall design.）。,1.3 流体传动系统的组成（COMPONENTS OF A FLUID POWER SYSTEM） 事实上所有的液压回路基本上是相同的与其使用无关。液压回路中由6个基本元件组成（Virtually

26、all hydraulic circuits are essentially the same regardless of the application. There are six basic components required in a hydraulic circuit）： 油箱（Tank）：盛装液体（通常是液压油）（A tank（reservoir）to hold the liquid, which is usually hydraulic oil）。 泵（Pump）：为系统中液体加载（A pump to force the liquid through the system）。

27、 电机或其它动力源（Motor or other power source）：驱动泵（An electric motor or other power source to drive the pump）。,控制阀（Control valve）：控制液体流动方向、压力和流量 （Valves to control liquid direction, pressure, and flow rate）。 执行元件（Actuator）：将液体能量转换为工作所需的力或力矩（实现直线运动的液压缸或实现旋转运动的液压马达）（An actuator to convert the energy of the li

28、quid into mechanical force or torque to do useful work. Actuators can be either cylinders to provide linear motion or motors（hydraulic） to provide rotary motion）。 管道（Piping）：使液体由一处流到另一处的管道（Piping which carries the liquid from one location to another）。 当然，液压系统的复杂程度和组成根据其用途的差异而不同。液压系统组成中包括特殊元件也是可以的,（O

29、f course, the sophistication and complexity of hydraulic systems will vary depending on the specific application. This is also true of the individual components which comprise the hydraulic system）。,1.4 流体传动系统的类型（TYPES OF A FLUID POWER SYSTEM） 我们已经知道了包括液压和气压系统的两种流体传动。流体传动能进一步细分为两种类型：开环（开式）和闭环（闭式）系统（

30、We have already established that fluid power includes both hydraulic and pneumatic systems. The field of fluid power can be further subdivided into two additional major categories: open-loop and closed-loop systems）。 闭环系统（Closed-loop system）：有反馈的。系统输出端的状况自动地反馈到输入端或被称为反馈传感器的装置，该装置产生控制信号。如果控制信号和反馈信号不同

31、，直到它对比了需求后装置将得到正确的系统输出施加于系统。闭环系统时常称为“伺服系统”，并且常常直接称控制执行元件的阀为“伺服阀” （A closed-loop,system is one which uses feedback. This means that the state of the output from the system is automatically sampled and compared（fed back） to the input or command signal by means of a device called a feedback transducer. If there is a difference between the command and feedback signals, action is taken to correct the system output until it matches the requirement imposed on the system. Closed-loop system are frequently called servo system,