Lesson 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 unit. Three different basic circuits are ud, 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 returns to the tank and in neutral the oil bypass 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 clod loop circuit h
as the exhaust oil returned to the pump suction. The pump is of the variable delivery type, providing maximum flexibility in oil supply to the equipment. Low pressure systems u 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 u. Medium pressure systems are favored for marine applications using either the open or clod 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 u 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 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 cas power is continuously transmitted 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 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 defined 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 convert the hydraulic energy into linear force and motion (mi-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 circuits 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 cas, the pumping action is achieved with reciprocating pistons and in the majority of designs variable output flow capacity is readily obtained—the 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 caus the pistons 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 caus the piston to move downwards; this expels fluid through the outlet port. Both the rotor face and the “slipper pads” on the piston’s ends are pressure balanced and lubricated to minimize power loss. 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 reverd.
