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1、LessonLesson 18 18SteeringSteering geargear(舵机、操舵装置舵机、操舵装置)Jimei universityThe steering gear is one of the most important services in the ship and its main function is to control the ships course.Jimei universityThere are four main types of steering gears employed for power operation of the rudder(舵
2、叶舵叶),Jimei university(i)the steam steering gear,(ii)the hydraulic steering gear,(iii)the electric steering gear and(iv)the electro-hydraulic steering gear.Jimei universityThe total system may be considered made up of three parts:control equipment,a power unit and a transmission to the rudder stock(舵
3、杆舵杆).Jimei universityRudderRudder stockTransmissionunitPower unitControl equipmentTillerJimei universityThe first part conveys(传传递递)a signal or desired rudder angle from the bridge(wheel house).Jimei universityThe second one provides the force,when required,to move the rudder to that angle.Jimei uni
4、versityThe third is the means by which the movement of the rudder is accomplished.Jimei universityAccording to the way the steering gear is operated,the steering gear may be divided into three kinds:hand-steering,followup(随随 动动)steering and automatic steering.Jimei universityThe electro-hydraulic ge
5、ar is now the most widely applied.Jimei universityA two ram(撞撞杆杆)hydraulic gear consists of a hydraulic ram situated on the port side of the tiller(舵舵柄柄)and another ram on the starboard side,Jimei universitylinked at their outer ends to the tiller arm by a crosshead and swivel block(转动滑块转动滑块),Jimei
6、universityRudderstockTiller armRamHunting gearCrosshead&swivel blockControl rodJimei universityCrosshead&swivel blockJimei universitythe other ends of the rams working inside their own hydraulic cylinders and pipes connect these cylinders to a hydraulic pump.Jimei universityThe tiller is firmly keye
7、d to the rudder stock.Jimei universityThe pump is of special construction and may be axial or radial design.Jimei universityThe pump runs continuously in the same direction driven by an electric motor,Jimei universityand the position of a movable plate or a floating ring inside the pump controls the
8、 suction and discharge of the oil.Jimei universityWhen the plate or ring is in mid position,no oil is drawn;Jimei universitywhen the plate or ring is moved in one direction from mid position,oil is drawn from one cylinder and discharged into the other;Jimei universitywhen the plate or ring is moved
9、in the opposite direction,the suction and discharge of the oil is reversed in direction.Jimei universityThe plate or ring is actuated by a control rod which is attached at its outer end to the hunting gear(随动机构随动机构).Jimei universityA four-ram hydraulic steering gear may be fitted in large ships for
10、greater steering power,instead of the two-ram type.Jimei universityJimei universityIt is simply a double two-ram unit,so that the force of two diagonally opposite rams can act on the tiller to produce double the turning effect.Jimei universityThe pump control is moved by the telemotor(液液压压传传动动操操舵舵装装
11、置置)through a floating lever.Jimei universityThe other end of this lever is connected through a safety spring link to the rudder stock or tiller.Jimei universityThe telemotor is the receiver of the hydraulic remote control system from wheel on the bridge.Jimei universityThe linkage through the floati
12、ng lever of telemoter,pump and rudder stock forms the hunting gear.Jimei universityThe pump is only required to deliver oil when the steering wheel is moved.Jimei universityThe hunting gear returns the pump operating rod to mid position as soon as the helmsman(舵舵 手手)stops turning the wheel.Jimei uni
13、versityWhen the rudder has moved through the angle corresponding to the wheel position,it will remain there until the wheel and telemotor are moved.Jimei universityIf a heavy sea strikes the rudder,the shock is transmitted through the tiller to the rams,this cause a sudden increase in oil pressure i
14、n one of the cylinders and the system.Jimei universityIf the pressure in the system rises to about 10 per cent above normal,double spring-loaded relief valves allow the tiller to give way slightly by by-passing a little of the oil into the other cylinder.Jimei universityThe resultant displacement of
15、 the rudder,tiller and ram crosshead moves the pump control rod through the hunting gear and the tiller is automatically brought back to its proper position.Jimei universityThe control equipment of steering gearsTelemotor control The telemotor has become,on many vessels,the standby steering mechanis
16、m,used only when the automatic steering fail.Jimei universityIt comprises a transmitter(发发送送器器),a receiver,pipes and a charging unit(充电装置充电装置).Jimei universityThe transmitter,which is built into the steering wheel console(舵舵轮轮控控制制台台),is located on the bridge and the receiver is mounted on the steeri
17、ng gear.Jimei universityTwo rams in the transmitter move in opposite directions as the steering wheel is turned.Jimei universityThe fluid in the cylinders of the transmitter is therefore pumped down one pipe line and drawn in from the other.Jimei universityThe pumped fluid passes through piping to t
18、he receiver and forces the telemotor cylinder unit to move.Jimei universityThe cylinder unit has a control spindle(轴轴)connected to it by a pin.Jimei universityThis control spindle operates the slipper ring or swash plate(倾倾斜斜盘盘)of the variable delivery pump,which controls the suction and discharge o
19、f the oil.Jimei universityElectrical control The electrical remote control system is commonly used in modern installations since Jimei universitysince it uses a small control unit as transmitter on the bridge and is simple and reliable in operation.Jimei universityThe control box assembly is mounted
20、 on the steering gear.Jimei universityMovement of the bridge transmitter results in electrical imbalance and current flow to the motor in the control box.Jimei universityThe motor drives,through a flexible coupling(柔柔性性联联轴轴节节),a screw shaft,causing it to turn.Jimei universityA screw block on the sha
21、ft is moved and in turn moves the floating lever to which a control rod is attached.Jimei universityThe control rod operates the slipper ring or swash plate of the variable delivery pump.Jimei universityA cut-off lever(反反 馈馈 杆杆)connected to the moving tiller will bring the floating lever pivot(枢枢 轴轴
22、，交交 点点)and the lever into line at right angles to the screw shaft axis(轴线轴线).Jimei universityAt this point the rudder angle will match the bridge lever angle and the pumping action will stop.Jimei universityFor local manual control,the electrical control is switched off and a small handwheel is conn
23、ected to the screw shaft.Jimei universityRotation of the handwheel will move the floating lever and bring about rudder movement as described.Jimei universitySteering gear testing Prior to a ships departure from any port the steering gear should be tested to ensure satisfactory operation.Jimei univer
24、sityThese tests should be:1.Operation of the main steering gear.2.Operation of the auxiliary steering gear or use of the second pump which acts as the auxiliary.Jimei university3.Operation of the remote control(telemotor)system or systems from the main bridge steering positions.Jimei university4.Ope
25、ration of the steering gear using the emergency power supply.Jimei university5.The rudder angle indicator reading with respect to the actual rudder angle should be checked.Jimei university6.The alarms fitted to the remote control system and the steering gear power units should be checked for correct
26、 operation.Jimei universityDuring these tests the rudder should be moved through its full travel in both directions and Jimei universityand the various equipment items,linkages,etc,visually inspected for damage or wear.Jimei universityThe communication system between the bridge and the steering gear
27、 compartment should also be operated.Jimei universityREADING MATERIAL A.HYDRAULIC MOTORS Jimei universityMost designs of positive displacement mechanism are capable of acting as pump or motor.Jimei universityThe principles of pumping have been described previously,but if instead of driving the shaft
28、,Jimei universityfluid is introduced into the inlet port at some pressure then in many designs the mechanism will rotate and in turn drive the shaft.Jimei universityExternal Gear,Vane and Axial Piston geometries are generally reversible,with detailed design differences between pumps and motors to ac
29、hieve optimum performance in each case.Jimei universitySpeeds achieved are comparable with pumps but without the practical restrictions(限限制制)imposed by a prime mover,speeds up to 4,000 or 6,000 r/min are possible with smaller sizes.Jimei universityOutput torques vary between 21 n mile(15 lbf ft)and
30、1,360 n mile(1,000 lbf ft)for a typical range of piston motors.Jimei universityObviously,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 acceptable torque levels for winch drives f
31、or instance.Jimei universityThis arrangement can be entirely satisfactory but an alternative approach is also possible using equipment of inherently lower speed and higher output torque capacity.Jimei universitySlow Speed High Torque Motors A number of different designs of slow speed motors are avai
32、lable and are commonly used in marine systems such as winch drives.Jimei universityMost are generally of much higher capacity per revolution than the pump/motor types described above.Jimei universityOne of these designs is radial piston unit,such as five piston radial slow speed high torque motor,wi
33、th pistons and connecting rods,operated via a single throw eccentric(偏偏心心轮轮、轴轴).Jimei universityFlow of fluid to and from pistons is through the central pintle(枢轴、配油轴枢轴、配油轴).Jimei universityIn the latest designs of this motor,cam eccentricity(偏偏心心)can be varied through an independent hydraulic suppl
34、y,giving smoothly varying capacity.Jimei universityAn example of an alternative design is the radial piston multi-lobe(圆圆形形突突出出部部、凸凸角角)low speed high torque motor(内曲线式液压马达内曲线式液压马达).Jimei universityThis is similarly radial in operation but the pistons operate inwardly(在内部地在内部地),Jimei universitythe os
35、cillating(往往复复)movement being obtained from an internal multi-lobed cam profile(外外形形,轮廓轮廓)around the periphery.Jimei universityIn a typical example,eight pistons run against a six-lobe track(六曲段轨迹六曲段轨迹).Jimei universityTherefore,each of eight pistons makes six oscillations in each revolution.Jimei u
36、niversityOne feature of this type of motor is that the number of working pistons can be reduced by suitable internal porting,thus obtaining the step change in capacity referred to earlier.Jimei universityTypically,ranges of this type of motor are capable of developing between 500 n mile(350 lbf ft)t
37、o 40,000 n mile(30,000 lbf ft)Jimei universitywith maximum speeds of 500 and 100 r/min,respectively,with certain equipment,torques of 130,000 n mile(95,000 lbf ft)are available directly with a maximum speed of 16 r/min.Jimei universityB。HYDRAULIC CIRCUIT CONTROL VAVALEAny hydraulic circuit includes
38、a variety of valves to regulate pressure or flow conditions to control force,torque,speed and/or the direction of movement of system output.Jimei universityThe large range of alternative proprietary equipment available can be considered for convenience in three separate groups:Flow control,Pressure
39、control;Directional control.Jimei universityIn practice,all valves are available in alternative forms for mounting either directly into pipelines or on machined manifold blocks and baseplates.Jimei universityPressure Control Valve There are two main types of pressure control valve-relief and reducin
40、g,the basic difference being that the relief valve is closed by a spring,and the reducing valve opened by a spring.Jimei universityRelief valves are used to protect the system from over pressure and are of two main types-direct acting and pilot operated.Jimei universityThe direct acting relief valve
41、 is used for controlling low flows and may be used for pressures up to 172 bar(2,500lbf/in2).Jimei universityFor higher pressures and larger flows,pilot operated valves are used.Jimei universityThis type of valve,in conjunction with a variable orifice and suitable circuitry(线线路路，回回路路),can be used fo
42、r bleed off(泄泄放放，溢溢流流，泄泄压压)control.Jimei universityThe pressure at which the valve opens and controls can be adjusted by the preload of the pilot valve spring.Jimei universityReducing valves are used to limit the pressure in any particular portion of the circuit,and again may be of direct acting or
43、pilot operated types.Jimei universityDirect 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.Jimei universityPilot operated units are used for greater flow,and to limit the pressure a
44、pplied to certain equipment in the circuit.Jimei universityWhen used in conjunction with a suitable orifice,they may also be used to control or limit flow as well as pressure.Jimei universityFlow Control ValveThere are three main variants of this type of control.Restrictor(节节流流阀阀，限限制制器器),a simple ne
45、edle valve,creating a variable restriction,effectively controls flow.Jimei universityA significant disadvantage of this control however,is that the flow is directly dependent upon pressure,I.e.load and hence no unique relationship exits between valve opening and flowrate.Jimei universityAccurate con
46、trol of part speed may be very difficult to achieve as the pressure is changed.Jimei universityThe disadvantage mentioned above can be overcome by using series flow control valves.Jimei universitySeries flow control valves are used where a number of operations have to be carried out from one pumping
47、 set.The valve functions in a similar way to the reducing valve.Jimei universityWith a orifice downstream,any variation in the flow through the orifice causes a variation in pressure drop across the both ends of the main valve piston andJimei universityand this,in turn,causes the main piston to take
48、 up a new position to restore the pressure drop across the valve opening and flow to the original setting.Jimei universityThe bleed-off flow control valve is basically similar to the pilot operated relief valve and is used in conjunction with an orifice in the supply line.Jimei universityThe valve c
49、an restore the pressure drop across the orifice to the original valve.Hence,the flowrate is not dependent upon working pressure level.Jimei universityDirection Control ValveThese valves,as their name implies,control the direction of flow of the fluid in the system,and are of three main types:1.Posit
50、ive seated type in which a ball or piston moves on or off the seat;Jimei university2.Rotary spool(滑滑阀阀阀阀芯芯)type in which the spool rotates about its own axis;3.Sliding spool type in which the spool moves axially in bore.This is by far the most common arrangement.Jimei universitySliding spool type va