Lesson 20 The Hydraulic System and Equipment.docx

1、Lesson 20 The Hydraulic System and EquipmentLesson 20 The Hydraulic System and Equipment第20 课 液压系统和液压设备Hydraulic Systems液压系统Hydraulic systems are made up of an oil tank, pumps, control valve, hydraulic motor and pipe work. The oil tank and pump is common to all equipment acting as a central pumping

2、unit. Three different basic circuits are used, employing either low or medium pressure oil supplies.液压系统由油箱、油泵、控制阀、液压马达和管路构成。油箱和油泵作为中央泵组，为所有设备公用。无论是低压还是中压供油单元中，都采用三种基本的回路。The open loop circuit takes oil from the tank and pumps it through a control valve into the hydraulic motor. The exhaust oil retu

3、rns to the tank and in neutral the oil bypasses the hydraulic motor. The live line circuit maintains a high pressure from which the control valve draws pressurized oil to the hydraulic motor as and when required. The closed loop circuit has the exhaust oil returned to the pump suction. The pump is o

4、f the variable delivery type, providing maximum flexibility in oil supply to the equipment. Low pressure systems use the open loop circuit and are simple in design as well as reliable. The equipment is however large, inefficient in operation and overheats after prolonged use. Medium pressure systems

5、 are favored for marine applications using either the open or closed circuit. Smaller installations are of the open loop circuit type.开式回路从油箱吸油，并经过控制阀将油泵送到液压马达。排油回到油箱，在中位时，经过液压马达油液旁通。在需要的情况下，根据液压系统的要求，控制阀将压力油送至液压马达，这部分液压管路一直保持高压。在闭式回路中排油回到泵的吸入口。油泵是变量式油泵，使得向设备的供油有了极大的灵活性。低压系统多采用开式回路，并且设计简单，工作可靠。然而设备体

6、积大，操作效率低，长时间运行会发热。船用装置中，无论是开式回路还是闭式回路，采用中压系统都是最适合的。小型装置采用开式回路。Many reasons can be suggested for the use of hydraulic systems in marine engineering:轮机工程方面采用液压系统的理由：(a) A convenient method of transferring power over relatively long distances from, say, a central pump room to remote operating sites in

7、the ship: where necessary, complete local control of operations can be achieved;A.在相当长的距离上，比如说从船上的中央泵到遥控处所，是方便的传动方式，当必要时可以实现完全的机旁控制。(b) Fully variable speed control of both linear and rotary motion, with good “inching” capability and smooth take up of load; In all cases power is continuously transmi

8、tted whilst speed changes take place;B.在直线运动和回转运动上可以实现无级变速，具有良好的微速性能和平稳的负载能力，在任何变速情况下都可以连续地传递动力。(c) High static forces or torques can be achieved and maintained indefinitely；C.可以实现并长时间保持静态力或者静扭矩(d) Complete safety and reliability is assured under the most difficult environmental conditions; overload

9、 conditions are safeguarded by using a relief valve to limit maximum output torques or forces;(的).在最恶劣环境下可以保证安全性和可靠性；通过使用安全阀限制最大力矩或最大力的输出从而防止超负荷。(e) Significant cost savings can be shown over alternative solutions for many requirements. In practical terms, four main categories of equipment can be de

10、fined in order to achieve this power transmission:E.为满足这些需要，与其他替代方案比较可以节约大量的成本，实际上，可以定义4种实现(液压)传动所需的主要设备：(i) The hydraulic pump to convert mechanical into hydraulic energy；(i)液压泵将机械能转变为液压能；(ii) Valves to allow this hydraulic energy to be controlled；(ii)阀件使得液压能得到控制；(iii) Hydraulic cylinders to conver

11、t the hydraulic energy into linear force and motion (semi-rotary actuators achieve part rotation)；(iii) 液压缸将液压能转变为直线的力和运动(半回转执行器可以实现部分回转运动)；(iv) Hydraulic motors to convert the hydraulic energy into continuous rotary motion.Although systems are designed to suit particular applications, basic circuit

12、s can be identified which illustrate the main principles and alternative types.(iv) 液压马达将液压能转变为连续的回转运动。虽然系统的设计适用于特定的装置，然而还是可以看出说明主要原理的基本回路和其他可选形式。Axial Piston Pumps轴向柱塞泵和轴向柱塞马达A number of basic types of piston equipment are available. In all cases, the pumping action is achieved with reciprocating p

13、istons and in the majority of designs variable output flow capacity is readily obtainedthe method depending upon the detailed geometry of the machine. The simplest design is usually described as the swashplate type and the concept is illustrated in Fig. 20-1.有多种基本形式的柱塞设备可供使用。在所有的情况下，抽吸作用是通过活塞的往复运动实现

14、的，在大多形式中可以实现变流量输出，变量方式依赖于机器的具体形状。最简单的形式通常被称作倾斜盘式，其原理如图20-1所示。Multiple pistons are positioned axially in a rotor, which is connected to the prime mover via the drive shaft. As the rotor revolves, the cylinders follow the path of the kidney-shaped inlet port. The angle of the swashplate causes the pis

15、tons to move in the cylinder bores away from the kidney port, thus allowing fluid to enter the cylinder. Further movement brings the cylinder on to the path of the outlet kidney port and causes the piston to move downwards; this expels fluid through the outlet port. Both the rotor face and the “slip

16、per pads” on the pistons ends are pressure balanced and lubricated to minimize power losses. With variable capacity units the angle of the swashplate is altered and the output flow varied proportionally. If the swashplate is moved “over center”, the direction of the flow is reversed.多个柱塞轴向布置在转子内，转子通

17、过驱动轴与原动机相连。当转子转动时，柱塞缸沿肾形进油口运动。倾斜盘的角度使得柱塞在柱塞缸内孔中运动远离腰形口，这样使得液体进入缸内。进一步的转动使柱塞缸沿肾形出口运动，并使柱塞向下运动，这样通过出口排出液体。转子端面和柱塞端部的滑块都压力平衡并且得到润滑，以尽量减小功率损失。通过变量机构改变倾斜盘的角度，输出流量就会按比例改变。如果倾斜盘移动超过中位，液流的方向将会改变。The basic simplicity of this type of equipment allows a compact variable capacity unit to be produced capable of

18、operating as pump or motor in either direction of rotation. The control can be readily adapted for operation by means of hand wheels or levers or for remote actuation by electrical, hydraulic or pneumatic signals. Also, a range of automatic or semiautomatic controls can be incorporated to simplify t

19、he operators task and improve safety whilst increasing work rates.这种设备的简单性使得紧凑的变量设备可以作为泵或者马达在任一方向上回转。控制易于通过手轮或者控制杆实现，或者通过远距离的电动、液压、气动信号驱动实现。另外，还可以包括一系列自动或者半自动的控制元件以简化操作者的任务，提高工作效率同时提高安全性。A second form of swashplate pump employs a stationary block carrying the pistons which are oscillated through a r

20、otating swashplate mechanism. Input and output flow passes through non-return valves connected to the individual cylinders.另一种倾斜盘泵采用一个静止的缸体，缸体内的柱塞由旋转的倾斜盘机构带动往复运动，液流通过与各缸相连的单向阀吸入和排出。The third form is particularly well established in Continental Europe. In this design the rotating cylinder barrel or r

21、otor is tilted (together with the porting faces) at an angle to the input drive shaft to produce the basic piston oscillation.第三种形式在欧洲大陆应用广泛。这种形式中，旋转的缸体即转子(与配油口平面一起)与输入轴成一定角度倾斜，这样产生活塞的往复运动。This design produces particularly compact fixed capacity units but leads to greater bulk with variable capacity

22、 types, since the complete rotor bearing assembly has to be swung about the drive axis.既然整个转子轴承组件不得不绕驱动轴摆动，这种设计产生了特别的紧凑定量泵但是导致了不同排量泵的大量生产。Other equipment using eccentric cams for piston drive is usually of smaller capacity, but direct drive from an electric motor at 1, 440r/min is possible. With thi

23、s type of pump pressures exceeding 690 bar (10, 000 lbf/in2) are regularly achieved.另有用偏心凸轮驱动柱塞的装置，通常体积较小，但可以由1440r/min转速的电机直接驱动。这种形式的泵通常可以实现超过690 bar (10000 磅)的高压。Motors马达Most designs of positive displacement mechanism are capable of acting as pump or motor. The principles of pumping have been desc

24、ribed above but if instead of driving the shaft, fluid is introduced into the inlet port at some pressure then in many designs the mechanism will rotate and in turn drive the shat The efficiency achieved for this action depends upon the mechanical arrangement.大多数形式的容积式装置可以用作泵或者马达。泵的原理前面己经说过，然而，如果不是驱

25、动轴(转动)，而是将油液以一定的压力引入进口，那么大多数形式的装置将会旋转，从而带动轴(转动)。这样实现的效率依赖于机械布置。Several particular unit designs are widely employed. Obviously, the relatively low output torque from the majority of pump motor equipment results in the requirement for some form of speed reduction gearbox in many cases to achieve accep

26、table torque levels for winch drives for instance. This arrangement can be entirely satisfactory but an alternative approach is also possible using equipment of inherently lower speed and higher output torque capability. A number of different designs of “slow speed” motors are available and are comm

27、only used in marine systems such as winch drives.然而某些广泛使用的形式中，是不允许反转的，这将在后面讲述。外齿轮式、叶片式和轴向柱塞式的几何结构通常是可逆使用的，它们在用作泵和马达时具有细节上的差别以在各自用途下获得较好的性能。显然，由于大多数泵用作马达时产生的扭矩输出相对较低，这使得在很多情况下需要某种形式的减速齿轮箱以获得可接受的扭矩，比如用于驱动绞盘时。这样的布置完全可以令人满意，但另一种方法是使用自身具有低转速、大扭矩输出的设备。Pressure Control Valves压力控制阀There are two main types o

28、f pressure control valverelief and reducing. The basic difference being that the relief valve is closed by a spring, and the reducing valve opened by a spring.压力控制阀主要有两种：安全阀和减压阀，它们基本的区别是，安全阀由弹簧关闭，而减压阀由弹簧打开。(a) Relief Valves(a)安全阀These are used to protect the system from over pressure. The direct act

29、ing relief valve is used for controlling low flows up to 172 bar (2, 500 lbf/in2) or higher. For higher pressures and larger flows, pilot operated valves are used. This type of valve, in conjunction with a variable orifice and suitable circuitry, can also be used for bleed-off control.The pressure a

30、t which the valve opens and controls can be adjusted by altering the preload of the pilot valve spring.安全阀用来保护系统以免超压。直接作用式安全阀用于172 bar 或者压力更高些的小流量系统，对于更高压力的大流量系统，采用先导式安全阀。这种形式的阀装有可调节流孔和适当的回路，也可以用作溢流控制。启阀压力和控制压力可以通过改变先导阀弹簧的预加载负荷来进行调整。(b) Reducing Valves (b)减压阀These are used to limit the pressure in a

31、ny particular portion of the circuit, and again may be of direct acting or pilot operated types.Direct acting valves are used mainly for providing a low flow and reduced pressure for pilot operation of other valves and for certain types of remote or sequencing control.Pilot operated units are used f

32、or greater flows, and to limit the pressure applied to certain equipment in the circuit. When used in conjunction with a suitable orifice, they may also be used to control or limit flow as well as pressure.减压阀用于限制回路中的某一部分的压力，同样可能以是直接作用式或者是先导式的。直接作用式减压阀主要用于提供小流量的减压压力，用于其他阀件的控制操作以及某些形式的遥控或者顺序控制。先导式减压阀用于较大流量场合，并且限制回路中施加于某些设备的压力。当与合适的孔口配合使用时，它们除了用于控制限制压力，同样也可以用来控制或者限制流量。Flow Control Valves流量控制阀There are three main variants of this type of control.主要有三种流量控制阀：(a) Restrictor(a)节流阀A simple needle valve, creating a variable restriction effectively controls flow if