专业英语15Word文档格式.docx

专业英语15Word文档格式.docx

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Withthetrailerkingpinuncoupled.thejawwillbeheldopenbythepawlinreadinessforcoupling（Fig.1.24（a））.Whencouplingthetractortothetrailer,thejawofthefifthwheelstrikesthekingpinofthetrailerandswivelsthejawaboutitspivotpinagainstthereturnspring,slightlypushingoutthepawl（Fig.1.24（b））.Furtherrearwardmovementofthetractortowardsthetrailerwillswingthejawrounduntilittrapsandenclosesthekingpin.Thespringloadnotchedpawlwillthensnapoverthejawprojectiontolockthekingpininthecouplingposition（Fig.1.24（c））.Thesecuringpinshouldthenbeinsertedthroughthepullleverandtableeyeholes.Whenthetractorisdrivingforward,thereactiononthekingpinincreasesthelockingforcebetweenthejawprojectionandthenotchedpawl.

Todisconnectthecoupling,liftoutthesecuringpinandpullthereleasehandleverfullyout（Fig.1.24（d））.Withboththetractorandtrailerstationary,themajorityofthelockingforceappliedtonotchedpawlwillberemovedsothatwithverylittleeffort,thepawlisabletoswingclearofthejawinreadinessforuncoupling,thatis,byjustdrivingthetractorawayfromthetrailer.Thusthejawwillsimplyswivelallowingthekingpintopulloutandawayfromthejaw.

1.4Trailerandcaravandrawbarcouplings

1.4.1Eyeandboltdrawbarcouplingforheavygoodstrailers（Figs1.25and1.26）

Drawbartrailersarenormallyhitchedtothetruckbymeansofan¡

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A¡

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framedrawbarwhichiscoupledbymeansofatowingeyeformedontheendofthedrawbar（Fig.1.25）.Whencoupled,thetowingeyeholeisalignedwiththeverticalholesintheupperandlowerjawsofthetruckcouplingandaneyeboltpassesthroughbothcouplingjawsanddraw-bareyetocompletetheattachment（Fig.1.26）.Lateraldrawbarswingispermittedowingtotheeyeboltpivotingactionandtheslotsbetweenthejawsoneitherside.Aligningthetowingeyetothejawsismadeeasierbytheconvergingupperandlowerlipsofthejawswhichguidethetowingeyeasthetruckisreversedandthejawsapproachthedrawbar.Isolatingthecouplingjawsfromthetruckdrawbeamaretworubberblockswhichactasadampingmediabetweenthetowingvehicleandtrailer.Theserubberblocksalsopermitadditionaldeflectionofthecouplingjawshaftrelativetothedrawbeamunderroughabnormaloperatingconditions,thuspreventingover-strainingthedrawbarandchassissystem.

Thecouplingjaws,eyeboltandtowingeyearegenerallymadefromforgedmanganesesteelwithinductionhardenedpressureareastoincreasethewearresistance.

Operationoftheautomaticdrawbarcoupling

（Fig.1.26）Intheuncoupledpositiontheeyeboltisheldintheopenpositionreadyforcoupling（Fig.1.26（a））.Whenthetruckisreversed,thejawsofthecouplingslipoverthetowingeyeandintheprocessstriketheconicallowerendoftheeyebolt（Fig.1.26（b））.Subsequently,theeyeboltwilllift.Thistripsthespring-loadedwedgeleverwhichnowrotatesclockwisesothatitbearsdownontheeyebolt.Furtherinwardmovementoftheeyeboltbetweenthecouplingjawsalignsthetowingeyewiththeeyebolt.Thespringpressurenowactsthroughthewedgelevertopushtheeyeboltthroughthetowingeyeandthelowercouplingjaw（Fig.1.26（c））.Whentheeyeboltstop-platehasbeenfullyloweredbythespringtension,thewedgeleverwillslotintoitsgrooveformedinthecentreoftheeyeboltsothatitlockstheeyeboltinthecoupledposition.

Touncouplethedrawbar,thehandleispulledupwardsagainstthetensionofthecoilspringmountedonthewedgeleveloperatingshaft（Fig.1.26（d））.Thisunlocksthewedge,freeingtheeyeboltandthenraisestheeyebolttotheuncoupledpositionwherethewedgeleverjamsitintheopenposition（Fig.1.26（a））.

1.4.2Ballandsockettowingbarcouplingfor

lightcaravan/trailers（Fig.1.27）

Lighttrailersorcaravansareusuallyattachedtotherearofthetowingcarbymeansofaballandsockettypecoupling.Theballpartoftheattachmentisboltedontoabracingbracketfitteddirectlytothebootpanorthetowingloadmaybesharedoutbetweentwosidebracketsattachedtotherearlongitudinalbox-sectionmembersofthebody.

Asinglechannelsectionorpairoftriangularlyarrangedangle-sectionarmsmaybeusedtoformthetowbarwhichbothsupportsanddrawsthetrailer.

Attachedtotheendofthetowbaristhesockethousingwithaninternallyformedsphericalcavity.Thisfitsovertheballmemberofthecouplingsothatitformsapivotjointwhichcanoperateinboththehorizontalandverticalplane（Fig.1.27）.

Tosecurethesocketovertheball,alockdevicemustbeincorporatedwhichenablesthecouplingtobereadilyconnectedordisconnected.Thislockmaytaketheformofaspring-loadedhorizontallypositionedwedgewithagrooveformedacrossitstopfacewhichslipsunderneathandagainsttheball.Thewedgeisheldintheclosedengagedpositionbyaspring-loadedverticalplungerwhichhasahorizontalgroovecutononeside.Anuncouplingleverengagestheplunger¡

sgroovesothatwhenthecouplingisdisconnectedtheleverissqueezedtoliftandreleasetheplungerfromthewedge.Atthesametimethewholetowbarisraisedbythehandletoclearthesocketandfromtheballmember.

Couplingthetowbartothecarsimplyreversestheprocess,theuncouplingleverisagainsqueezedagainstthehandletowithdrawtheplungerandthesockethousingispusheddownovertheballmember.Thewedgemovesoutwardsandallowstheballtoenterthesocketandimmediatelythewedgespringsbackintotheengagedposition.Releasingtheleverandhandlecompletesthecouplingbypermittingtheplungertoenterthewedgelockgroove.

Sometimesastrongcompressionspringisinterposedbetweenthesockethousingmemberandthetowing（draw）bartocushiontheshockloadwhenthecartrailercombinationisinitiallydrivenawayfromastandstill.

1.5Semi-trailerlandinggear（Fig.1.28）

Landinglegsareusedtosupportthefrontofthesemi-trailerwhenthetractorunitisuncoupled.

Extendablelandinglegsareboltedverticallytoeachchassisside-memberbehindtherearwheelsof

thetractorunit,justsufficientlybacktoclearthereartractorroadwheelswhenthetraileriscoupledandthecombinationisbeingmanoeuvred（Fig.1.28（a））.Toprovideadditionalsupportforthelegs,bracingstaysareattachedbetweenthelegsandfromthelegsdiagonallytothechassiscross-member（Fig.1.28（b））.

Thelegsconsistofinnerandouterhightensilesteeltubesofsquaresection.Ajackscrewwithabevelwheelattachedatitstopendsupportedbytheouterleghorizontalplateinabronzebushbearing.Thejawscrewfitsintoanutwhichismountedatthetopoftheinnerlegandataperrollerbearingraceisplacedunderneaththeouterleghorizontalsupportplateandtheupperpartofthejackscrewtominimizefrictionwhenthescrewisrotated（Fig.1.28（b））.Thebottomendsoftheinnerlegsmaysupporteithertwinwheels,whichenablethetrailertobemanoeuvred,orsimplyflatfeet.Thelatterareabletospreadtheloadandsopermitgreaterloadcapacity.

Toextendorretracttheinnerlegs,awindinghandleisattachedtoeithertheloworhighspeedshaftprotrudingfromthesideofthegearbox.Theupperhighspeedshaftsupportsabevelpinionwhichmesheswithaverticallymountedbevelwheelformingpartofthejackscrew.

Rotatingtheuppershaftimpartsmotiondirectlytothejackscrewthroughthebevelgears.Ifgreaterleverageisrequiredtoraiseorlowerthefrontofthetrailer,thelowershaftisengagedandrotated.Thisprovidesagearreductionthroughacompoundgeartraintotheuppershaftwhichthendrivesthebevelpinionandwheelandhencethejackscrew.

1.6Automaticchassislubricationsystem

1.6.1Theneedforautomaticlubricationsystem

（Fig.1.29）

Owingtotheheavyloadstheycarrycommercialvehiclesstillprefertousemetaltometaljointswhichareexternallylubricated.Suchjointsarekingpinsandbushes,shacklepinsandbushes,steeringballjoints,fifthwheelcoupling,parkingbrakelinkageetc.（Fig.1.29）.Thesejointsrequirelubricatinginproportiontotheamountofrelativemovementandtheloadsexerted.Iflubricationistobeeffectiveinreducingwearbetweenthemovingparts,freshoilmustbepumpedbetweenthejointsfrequently.Thiscanbestbeachievedbyincorporatinganautomaticlubricationsystemwhichpumpsoiltothebearing¡

ssurfacesinaccordancetothedistancetravelledbythevehicle.

1.6.2Descriptionofairdromicautomaticchassislubricationsystem（Fig.1.30）

Thislubricationsystemcomprisesfourmajorcomponents;

acombinedpumpassembly,apowerunit,anoilunloadervalveandanaircontrolunit.

Pumpassembly（Fig.1.30）Thepumpassemblyconsistsofacircularhousingcontainingaratchetoperateddrive（cam）shaftuponwhicharemountedone,twoorthreesinglelobecams（onlyonecamshown）.Eachcamoperatesarowof20pumpingunitsdisposedradiallyaroundthepumpcasing,theunitsbeingconnectedtothechassisbearingsbynylontubing.

Powerunit（Fig.1.30）Thisunitcomprisesacylinderandspring-loadedairoperatedpistonwhichismountedonthefrontfaceofthepumpassemblyhousing,thepistonrodbeingconnectedindirectlytothedriveshaftratchetwheelbywayofaratchethousingandpawl.

Oilunloadervalve（Fig.1.30）Thisconsistsofashuttlevalvemountedonthefrontofthepumpassemblyhousing.Theoilunloadervalveallowsairpressuretoflowtothepowerunitforthepowerstroke.Duringtheexhauststroke,however,