《新版輪機(jī)英語(yǔ)unit23課部分課件》由會(huì)員分享，可在線閱讀，更多相關(guān)《新版輪機(jī)英語(yǔ)unit23課部分課件（104頁(yè)珍藏版）》請(qǐng)?jiān)谘b配圖網(wǎng)上搜索。
1、23 The Hydraulic System and Equipment Hydraulic systems Hydraulic systems are made up of an oil tank(油箱）, pumps, control valves, hydraulic motor and pipe work. The oil tank and pump are common（共有的） to all equipment acting as a central pumping unit(單元，裝置，單位）. Three different basic circuits are used,
2、employing either low or medium pressure oil supplies（供油單元）. The open loop circuit（開(kāi)式回路） 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（中位） the oil bypasses the hydraulic motor. The live line circuit maintains
3、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 of the variable delivery type, providing maximum flexibility in oil supply to the equipment. Low press
4、ure system 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 are favored for marine application using either the open or closed circuit. Smaller installations are
5、 of the open loop circuit type. Many reasons can be suggest for the use of hydraulic systems Marine engineering: (a) A convenient method of transferring power（傳動(dòng)） over relatively long distance from, say, a central pump room to remote（遙遠(yuǎn)的） operating sites in the ship: where necessary, complete local
6、control of operations can be achieved; (b) Fully variable speed control（無(wú)極變速） of both linear（直線的） and rotary motion（回轉(zhuǎn)運(yùn)動(dòng)）, with good “inching” capability（微速性能） and smooth（平穩(wěn)的） take up of load; in all cases power is continuously transmitted whilst speed changes take place; (c) High static force（靜態(tài)力）
7、or torques（力矩） can be achieved and maintained indefinitely（無(wú)限期的）; (d) Complete safety and reliability is assured under the most difficult environment conditions; overload conditions are safeguarded by using a relief valve to limit maximum output torques or forces; (e) Significant cost savings can be
8、 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： (1) The hydraulic pump to convert mechanical into hydraulic energy; (2) Valves（閥件） to allow this hydraulic energy to be controlle
9、d; (3) Hydraulic cylinders to convert the hydraulic energy into linear force and motion (semi-rotary achieve part rotation); (4) Hydraulic motors to convert the hydraulic energy into continuous rotary motion. Although system are designed to suit particular applications, basic circuits can be identif
10、ied which illustrate the main principles and alternative types. Axial piston pumps and motors A number of basic types of piston equipment（柱塞設(shè)備） are available. In all cases, the pumping action is achieved with reciprocating（往復(fù)的） pistons and in the majority of designs variable output flow capacity is
11、readily obtained -the method depending upon the detailed geometry（幾何學(xué)） of the machine. The simplest design is usually described as the swashplate type(傾斜盤(pán)式） and the concept is illustrated in Fig.23-1. Multiple pistons are positioned axially（向軸的方向） in a rotor, which is connected to the prime mover vi
12、a the drive shaft（驅(qū)動(dòng)軸）. As the rotor revolves, the cylinders follow the path of the kidney-shaped（腎形） inlet port. The angle of the swasplate causes the pitons to move in the cylinder bores away from the kidney port, thus allowing fluid to enter the cylinder. Further movement brings the cylinder on t
13、o the path of the out kidney port and causes the piston to move downwards, this expels fluid through the outlet port. Both the rotor face and the “slipper pads” (滑塊） on the piston ends are pressure balanced and lubricated to minimize power losses. With variable capacity units（變量機(jī)構(gòu)） the angle of the
14、swashplate is altered and the output flow varied proportionally（按比例的）. If the swashplate is moved “over centre ”, the direction of the flow is reversed. The forces involved with small pumps allow the volume to be varied mechanically, but on the larger sizes the forces increase to such a magnitude（大小
15、，巨大） that some form of servo（伺服） assistance is essential. This takes the form of an internal piston（內(nèi)置活塞） operated through a simple servo arrangement and which takes its power from high pressure pump output . The basically simplicity of this type of equipment allows a compact variable capacity unit
16、to be produced capable of 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 semi-automatic controls can be
17、incorporated to simplify the operators task and improve safety whilst increasing work rates（工作效率） . A second form of swashplate pump employs a stationary block（缸體） carrying the pistons which are oscillated(振蕩） through a rotating swashplate mechanism. Input and output flow passes through non-return v
18、alves（單向閥） connected to the individual cylinders. The third form is particularly well established in Continental（大陸） Europe. In this design the rotating cylinder barrel(缸體） or rotor is tilted（傾斜的） (together with the porting faces) at an angle to the input drive shaft to produce the basic piston osci
19、llation（往復(fù)運(yùn)動(dòng)）. This design produces particularly compact fixed capacity units but leads to greater bulk with variable capacity types, since the complete rotor bearing assembly has to be swung（擺動(dòng)） about the drive axis. Other equipment using eccentric cams for piston drive is usually of smaller capaci
20、ty, but direct drive from an electric motor at 1440r/min is possible. With this type of pump pressures exceeding 690 bar(10,000lbf/in2) are regularly achieved. RADIAL PISTON PUMPS This type of pump is usually fixed capacity（排量） per revolution, with a single eccentric（偏心輪） but in some designs the ecc
21、entricity（偏心率） can be adjusted to vary output . It shows a particular design with a ball and poppet valve arrangement used to achieve an effective pumping action. This type of pump generally gives lower flows than other designs, but in simple geometry is capable of achieving high pressure ,e. g. up
22、to 414bar(6,000lbf/in2). Motors Most designs of positive displacement mechanism（容積式裝置） are capable of acting as pump or motor . The principles of pumping have been described above but if instead of driving the shaft, fluid is introduced into the inlet port at some pressure then in many designs the m
23、echanism will rotate and in turn drive the shaft. The efficiency achieved for this action depends upon the mechanical arrangement. Several particular unit designs are widely employed however where this “reversal” is not possible and these are described later. External Gear, Vane and Axial Piston geo
24、metries are generally reversible, with detailed design differences between pumps and motors to achieve optimum performance in each case. 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 c
25、ases to achieve acceptable torque levels for winch（絞盤(pán)） 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. Slow speed high torque motors A number of different d
26、esigns of “slow speed” motors are available and are commonly used in marine systems such as winch drives. Most are generally of much higher capacity per revolution than the pump motor types described above . Pressure control valves There are two main types of pressure control valve-relief (安全閥） and
27、the reducing， The basic difference being that the relief valve is closed by a spring, and the reducing value opened by a spring. (a) Relief valves These are used to protect the system from over pressure. The direct acting relief valve is used for controlling low flows up to 172bar (2,500lbf/in2) or
28、higher. For higher pressures and larger flows, pilot operated (先導(dǎo)式） valves are used . this type of valve, in conjunction with a variable orifice（節(jié)流孔） and suitable circuitry（回路）, can also be used for bleed off control（溢流控制）. The pressure at which the valve opens and controls can be adjusted by alteri
29、ng the preload（預(yù)載） of the pilot valve（導(dǎo)閥） spring . Reducing valves These are used to limit the pressure in any 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 op
30、eration（控制操作） of other valves and for certain types of remote or sequencing（順序） control. Pilot operated units are used for greater flows, and to limit the pressure applied to certain equipment in the circuit. When used in conjunction with a suitable orifice(孔）, they may also be used to control or li
31、mit flow as well as pressure. Flow control valves There are three main variants of this type of control. Restrictor(節(jié)流閥） A simple needle valve, creating a variable restriction effectively controls flow if used as control valve. A significant disadvantage of this control however, is that the flow is
32、directly dependent upon pressure（壓力）. i.e. load and hence no unique（唯一的） relationship exists between valve opening and ram（撞桿） speed. With high pressures, accurate （精確的）control of part speed conditions may be very difficult to achieve . Bleed-off flow control(溢流調(diào)速閥） This valve is basically similar t
33、o the pilot operated relief valve described above and is used in conjunction with an orifice in the supply line. 詳細(xì)符號(hào) 簡(jiǎn)化符號(hào) ) ( ) ( Series flow control (串聯(lián)調(diào)速閥） The series flow control with orifice downstream（下游的） functions in a similar way to the reducing valve. ) ( ) ( 詳細(xì)符號(hào) 簡(jiǎn)化符號(hào) The pressure drop cr
34、oss the orifice is measured and transferred to the ends of the piston with due allowance for the control spring. Any variation in the flow through the orifice causes a variation in pressure drop across it and this, in turn , causes the main piston（主活塞） to take up a new position to restore（使恢復(fù)） the p
35、ressure drop and flow to the original settings. The orifice may be a separate unit connected to the flow control valve by pipe work, or it may be included in the design of the valve block（閥體） as an integral unit. The orifice may be fixed or variable. Series flow control valves（串聯(lián)調(diào)速閥） are used where
36、a number of operations have to be carried out from one pumping set. It is usually necessary to operate the pump at maximum pressure which is set by the relief valve. Some oil must constantly flow through this valve and since this flow-at maximum pressure-constitutes waste, power problems can arise t
37、hrough oil overheating . Sequence valves（順序閥） While these units are often classed with pressure control valves they are basically a directional control valve arranged to operate at a certain pressure, which is usually adjustable. They are intended, according to the requirement, to either open or clo
38、se a secondary circuit(次級(jí)回路） during the cycle of operation. Some units（裝置） have an adjustable differential（可調(diào)偏差）, particularly conjunction with an accumulator unloading circuit(蓄壓卸荷回路）. Directional control valves These valves, as their name implies, control the direction of flow of the fluid in the
39、system, and are of three main types: (a) Positive seated type(閥座式） in which a ball or piston（柱塞） moves on or off the seat （b）Rotary spool type（轉(zhuǎn)閥式） in which the spool（閥芯） rotates about its own axis; （c）Sliding spool type（滑閥式） in which the spool moves axially in a bore（孔）; this is by far the most common arrangement and will therefore be considered in more detail.
新版輪機(jī)英語(yǔ)unit23課部分課件
