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Lesson26SteeringgearThedirectionoftheshipiscontrolledbythesteeringgear.Astheshipmovesthroughthewater,tileangleoftherudder(舵叶）atthestem（舵柱）determinesthedirectionitwillmove.Modernshiparesobigthatmovingtheruddernecessitatestheuseofhydraulicsorelectricalpower.Thesteeringgearprovidesamovementoftherudder（舵）inresponsetoasignal（信号）fromthebridge（驾驶台）.Thetotalsystemmaybeconsideredmadeupofthreeparts:controlequipment（控制设备）,apowerunit（动力单元）andatransmissiontotherudderstock（转舵机构）.Thecontrolequipmentconveysasignalofdesiredrudderangle（期望舵角）fromthebridgeandactivates（触发）thepowerunitandtransmissionsystemuntilthedesiredangleisreached.Thepowerunitprovidestheforce,whenrequiredandwithimmediateeffect,tomovetheruddertothedesiredangle.Thetransmissionsystemismeansbywhichthemovementoftherudderisaccomplished.Thesteering（操舵)startsatthebridge.therequiredrudderangleistransmittedhydraulicallyorelectricallyfromthesteeringwheelatthebridgetothetelemotor(液压传动操舵装置）atthesteeringgear,justabovetherudder.Thereareafewcommonarrangementsforusinghydraulicpower.Thereare4-rams（撞杆）,2-rams(fig.26-1)androtaryvanetypes（转叶式）.Theheartofthesehydraulicsystemsisthevariabledeliverypump（变量泵）.Thistypeofpumpcanbecontrolledbyjustmovingaspindle（控制杆）.Thepumpisdrivenbyanelectricalmotoratconstantspeed.Bymovingthecontrolspindleawayfromthecentralpoint,thepumpstrokeincreases,andthehydraulicfluidispumpedinonedirection.Movingthespindlemorefromthecentralpointwillcausemorefluidtobepumpedandconsequentlymorepressuregeneratedtodrivetherams（撞杆）.Movingthecontrolspindlebacktotheoriginalpositionandthenawayintheoppositedirectioncausesthehydraulicfluidtobepumpedinthereverseddirection.Theramswillalsomoveinthereverseddirection.Byusingafloatinglever（浮动杆）feedbackmechanism（反馈机构）,whentherudderstock（舵柱）hasreachedthedesiredangle,thepumpcontrollevermovesbacktotheoriginalposition,andthepumpingactionstops.Therudderisstoppedattherequiredangle.Movingthesteeringwheeltotheoppositedirectionwillcausetheruddertocomebacktotheoriginalzeroposition.Certainrequirements（要求）mustcurrently（目前的）bemetbyaship'ssteeringsystem.Theremustbetwoindependentmeansofsteering,althoughwheretwoidenticalpowerunitsareprovided,anauxiliaryunitisnotrequired.Thepowerandtorque（扭矩）capabilitymustbesuchthattheruddercanbeswung（旋转）from35°theothersidewiththeshipatmaximumspeed,andalsothetimetoswingfrom35°onesideto30°theothersidemustnotexceed28seconds.Thesystemmustbeprotectedfromshockingloading（冲击负载）andhavepipe-workwhichisexclusive（专用）toitaswellasbeconstructedfromapprovedmaterials（认可的材料）.Controlofthesteeringgearmustbeprovidedinthesteeringgearcompartment（舵机房）.Tankersof10,000tonsgrosstonnageandupwardsmusthavetwoindependentsteeringgearcontrolsystemwhichareoperatedfromthebridge.Whereonefails,changeovertotheothermustbeimmediateandachievedfromthebridgeposition.Thesteeringgearitselfmustcomprisetwoindependentsystemswhereafailureofoneresultsinanautomaticchangeovertotheotherwithin45seconds.Anyofthesefailuresshouldresultinanaudibleandvisualalarmsonthebridge.ElectricalcontrolTheelectricalremotecontrolsystemiscommonlyusedinmoderninstallations，andsmallcontrolunitastransmitter（发讯器）onthebridgeandissimpleandreliableinoperation.Thecontrolboxassembly（控制箱组件）ismountedonthesteeringgear.Movementofthebridgetransmitter（发讯器）resultsinelectricalimbalance（不平衡）andcurrentflowtothemotorinthecontrolbox.Themotordrives,throughaflexiblecoupling(柔性联轴节),ascrewshaft（螺杆）,causingittoturn.Ascrewblockontheshaftismovedandinturnmovesthefloatinglever（浮动杆）towhichacontrolrod（控制杆）isattached.Thecontrolrodoperatestheslipperring（滑环）orswashplate（斜盘）ofthevariabledeliverypump.Acut-offlever(反馈杆)connectedtothemovingtiller（移动舵柄）willbringthefloatingleverpivot(枢轴，交点)andtheleverintolineatrightanglestothescrewshaftaxis(轴线).Atthispointtherudderanglewillmatchthebridgeleverangleandthepumpingactionwillstop.Forlocalmanualcontrol,theelectricalcontrolisswitchedoffandasmallhandwheelisconnectedtothescrewshaft.Rotationofthehandwheelwillmovethefloatingleverandbringaboutruddermovementasdescribed.SteeringgeartestingPriortoaship’sdeparturefromanyportthesteeringgearshouldbetestedtoensuresatisfactoryoperation.Thesetestsshouldbe:1.Operationofthemainsteeringgear.2.Operationoftheauxiliarysteeringgearoruseofthesecondpumpwhichactsastheauxiliary.3.Operationoftheremotecontrol(telemotor)systemfromthemainbridgesteeringpositions.4.Operationofthesteeringgearusingtheemergencypowersupply（应急电源）.5.Therudderangleindicator（舵角指示器）readingwithrespecttotheactualrudderangleshouldbechecked.6.Thealarmsfittedtotheremotecontrolsystemandthesteeringgearpowerunitsshouldbecheckedforcorrectoperation.Duringtheseteststheruddershouldbemovedthroughitsfulltravelinbothdirectionsandandthevariousequipmentitems,linkages（连接）,etc,visuallyinspectedfordamageorwear.Thecommunicationsystem（通信系统）betweenthebridgeandthesteeringgearcompartmentshouldalsobeoperated.