液压系统-外文翻译

Hydraulic System

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 efficient 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 distances than are electrical systems.

Hydraulic power transmission system are concerned with the generation, modulation, and control of pressure and flow, and in general such systems include:

1.Pumps which convert available power from the prime mover to hydraulic power at the actuator.

2.Valves which control the direction of pump-flow, the level of power produced, and the amount of fluid-flow to the actuators. The power level is determined by controlling both the flow and pressure level.

3.Actuators which convert hydraulic power to usable mechanical power output at the point required.

4.The medium, which is a liquid, provides rigid transmission and control as well as lubrication of components, sealing in valves, and cooling of the system.

5.Connectors which link the various system components, provide power conductors for the fluid under pressure, and fluid flow return to tank (reservoir).

6.Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well as cooling of the fluid.

Hydraulic systems are used in industrial applications such as stamping presses, steel mills , and general manufacturing , agricultural machines , mining industry , aviation , space technology , deep-sea exploration ,transportation , marine

technology , and offshore gas petroleum exploration . In short, very few people get through a day of their lives without somehow benefiting from the technology of hydraulics.

The secret of hydraulic system’s success and widespread use is its versatility and manageability. Fluid power is not hindered 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 limited 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.

Industry is going to depend more and more on automation in order to increase 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.

Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power systems can readily start, stop, speed up or slow down, and position force which provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch.

Multiplication of force. A fluid power system (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.

Constant force or torque. 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 few revolutions per hour, or thousands of revolutions per minute.

Simplicity, safety, economy. In general, fluid power systems use fewer moving

parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, compactness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on many off-highway vehicles. The steering unit consists of a manually operated directional control valve and meter in a single body. Because the sterring unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, ect . are eliminated. This provides a simple,compact systems.In addition, very little input torque is required to produce the control needed for the toughest applications. This is important where limitations of control space require a small sterring wheel and it becomes necessary to reduce operator fatigue.

Additional benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of 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. Also, most hydraulic oils can cause fires if an oil leak occurs in area of hot equipment. 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 efficient 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 distances than are electrical systems.

Hydraulic power transmission system are concerned with the generation, modulation, and control of pressure and flow, and in general such systems include:

Pumps which convert available power from the prime mover to hydraulic power at the actuator.

Valves which control the direction of pump-flow, the level of power produced, and the amount of fluid-flow to the actuators. The power level is determined by controlling both the flow and pressure level.

Actuators which convert hydraulic power to usable mechanical power output at the point required.

The medium, which is a liquid, provides rigid transmission and control as well as lubrication of components, sealing in valves, and cooling of the system.

Connectors which link the various system components, provide power conductors for the fluid under pressure, and fluid flow return to tank (reservoir).

Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well as cooling of the fluid.

Hydraulic systems are used in industrial applications such as stamping presses, steel mills , and general manufacturing , agricultural machines , mining industry , aviation , space technology , deep-sea exploration ,transportation , marine technology , and offshore gas petroleum exploration . In short, very few people get through a day of their lives without somehow benefiting from the technology of hydraulics.

The secret of hydraulic system’s success and widespread use is its versatility and manageability. Fluid power is not hindered 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 limited 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.

Industry is going to depend more and more on automation in order to increase 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. Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power systems can readily start, stop, speed up or slow down, and position force which provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch.

2. Multiplication of force. A fluid power system (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. Constant force or torque. 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 few revolutions per hour, or thousands of revolutions per minute.

4. Simplicity, safety, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, compactness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on many off-highway vehicles. The steering unit consists of a manually operated directional control valve and meter in a single body. Because the sterring unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, ect . are eliminated. This provides a simple,compact systems.In addition, very little input torque is required to produce the control needed for the toughest applications. This is important where limitations of control

space require a small sterring wheel and it becomes necessary to reduce operator fatigue.

Additional benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of 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. Also, most hydraulic oils can cause fires if an oil leak occurs in area of hot equipment.

液压系统

仅有以下三种基本方法传递动力：电气，机械和流体。大多数应用系统实际上是将三种方法组合起来而得到最有效的最全面的系。为了合理的确定采取哪种方法，重要的是了解各种方法的显著特征。例如液压系统在长距离上比机械系统更能经济的传递动力。然而液压系统与电气系统相比，传递动力的距离较短。

液压动力传递系统涉及电动机，调节装置和压力和流量控制，总的来说，该系统包括：

泵：将原动机的能量转换成作用在执行部件上所谓液压能。

阀：控制泵产生流体的运动方向，产生的功率的大小，以及到达执行部件液体的流量。功率大小取决与对流量和压力大小的控制。

执行部件：将液压能转换成可用的机械能。

介质即油液：可进行无压缩传递和控制，同时可以润滑部件，使阀体密封和系统冷却。

联结件：联结各个系统部件，为压力流体提供功率传输通路，将液体返回油箱（贮油器）。

油液贮存和调节装置：用来确保提供足够质量和数量并冷却的液体。

液压系统在工业中应用广泛，例如冲压，钢类工件的磨削及一般加工业，农业，矿业，航天技术，深海勘探，运输，海洋技术，近海天然气和石油勘探等行业，简而言之，在日常生活中很少有人不从液压技术中得到某种益处。

液压系统成功而又广泛使用的秘密在于它的通用性和易作性。液压动力传递不会像机械系统那样受到机器几何形体的制约，另外，液压系统不会像电气系统那样受到材料物理性能的制约，它对传递功率几乎没有量的限制。例如，一个电磁体的性能受到钢的磁饱和极限的限制，相反，液压系统的功率仅仅受材料强度的限制。

企业为了提高生产率将越来越依靠自动化，这包括远程和直接控制生产操

作，加工过程和材料处理等。液压动力之所以成为自动化的重要组成分，是因为它有如下主要的四种优点：

1. 控制方便精确通过操作一个简单的操作杆和按钮，液压系统的操作者便能立即启动，停止，加减速和能提供任意功率，位置精度为万分之一英寸的位置控制力。

2. 增力一个液压系统（没有使用笨重的齿轮，滑轮和杠杆）

能简单有效地将不到一盎司的力放大产生几百吨力的输出。

3.恒力和恒扭矩只有液压系统能提供不随速度变化的恒力或恒扭矩，它可以驱动对象从每小时移动几英寸到每分钟几百英寸，从每小时几百转到每分钟几千转。

4. 简单，安全，经济总的来说，液压系统比机械或电气系统使用更少的运动部件，因此，它们运行与维护简单。这使的系统结构紧凑，安全可靠。例如一种用于车辆上的新型动力转向控制装置已淘汰其他类型的转向动力装置，该转向部件中包含有人力操作方向控制阀和分配器。因为转向部件是全液压的，没有万向节，轴承，减速齿轮等机械连接，这使得系统简单紧凑。

另外，只需输入很小的扭矩就能产生满足极恶劣工作条件所需的控制力，这对于因操作空间限制而需要方向盘的场合很重要，这也是减轻司机疲劳度所必需的。

液压系统的其他优点包括双向运动，过载保护和无级变速控制，在已有的任何动力系统中液压系统亦具有最大的单位质量功率比。

尽管液压系统具有如此高性能，但它不是可以解决所有动力传递问题的灵丹妙药。液压系统也有些缺点，液压油有污染，并且泄露不可能完全避免，另外如果油液渗漏发生在灼热设备附近，大多数液压油能引起火灾。

气压系统

气压系统是用压力气体传递和控制动力，正如名称所表明的那样，气压系统通常用空气（不用其它的气体）作为流体介质，因为空气是安全、成本低而

又随处可得的流体，在系统部件中产生电弧有可能点燃泄露物的的场合下（使用空气作为介质）尤其安全。

在气压系统中，压缩机用来压缩并供应所需的空气。压缩机一般有活塞式、叶片式和螺旋式等类型。压缩机基本上是根据理想气体法则，通过减小气体体积来增加气体压力的。气压系统通常考虑采用大的中央空气压缩机作为一个无限量的气源，这类似于电力系统中只要将插头插入插座便可获得电能。用这种方法，压力气体可以从气源输送到整个工厂的各个角落，压力气体可通过空气气滤器除去污物，这些污物可能会损坏气动组件的精密配合部件如阀和气缸等，随后输送到各个回路中，接着空气流经减压阀以减小气压值适合某一回路使用。因为空气

不是好的润滑剂（包括20%的氧气），气压系统需要一个油雾器将细小的油雾注射到经过减压阀减压的空气中，这有助于减少气动组件精密配合运动件的磨损。

由于来自大气中的空气含不同数量的水分，这些水分是有害的，它可以带走润滑剂引起过分磨损和腐蚀，因此，在一些使用场合中，要用空气干燥器来除去这些有害的水分。由于气压系统直接向大气排气，会产生过大噪音，因此可在气阀和执行组件排气口安装消声器来降低噪音，以防止操作人员因接触噪声及高速空气粒子有可能引发的危害。

用气动系统代替液压系统有以下几条理由：液体的惯性远比气体大，因此，液压系统中，当执行组件加速和减速和阀突然开启关闭时，油液的质量便是一个潜在的问题，根据牛顿运动定律（力等于质量乘以加速度），产生加速运动油液所需的力要比加速同等体积空气的力高出许多倍4。液体比气体具有更大的粘性，这会因为内摩擦而引起更大的压力和功率损失：另外，由于液压系统使用的液体要与大气隔绝，故他们需要特殊的油箱和无泄露系统设计。气压系统使用可以直接排到周围环境中的空气，一般来说气压系统没有液体系统昂贵。

然而，由于空气的可压缩性，使得气压系统执行组件不可能得到精确的速度控制和位置控制。气压系统由于压缩机局限，其系统压力相当低（地于250psi）,而液压力可达1000psi之高，因此液压系统可以是大功率系统，而气动系统仅用于小功率系统，典型例子有冲压、钻孔、提升、冲孔、夹紧、组装、镏接、材料处理和逻辑控制操作等。