氢动力线控技术.docx
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氢动力线控技术.docx
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氢动力线控技术
HowGM'sHy-wireWorks
Carsareimmenselycomplicatedmachines,butwhenyougetdowntoit,theydoanincrediblysimplejob.Mostofthecomplexstuffinacarisdedicatedtoturningwheels,whichgriptheroadtopullthecarbodyandpassengersalong.Thesteeringsystemtiltsthewheelssidetosidetoturnthecar,andbrakeandaccelerationsystemscontrolthespeedofthewheels.
Giventhattheoverallfunctionofacarissobasic(itjustneedstoproviderotarymotiontowheels),itseemsalittlestrangethatalmostallcarshavethesamecollectionofcomplexdevicescrammedunderthehoodandthesamegeneralmassofmechanicalandhydrauliclinkagesrunningthroughout.Whydocarsnecessarilyneedasteeringcolumn,brakeandaccelerationpedals,acombustionengine,acatalyticconvertorandtherestofit?
Accordingtomanyleadingautomotiveengineers,theydon't;andmoretothepoint,inthenearfuture,theywon't.Mostlikely,alotofuswillbedrivingradicallydifferentcarswithin20years.Andthedifferencewon'tjustbeunderthehood--owninganddrivingcarswillchangesignificantly,too.
Inthisarticle,we'lllookatoneinterestingvisionofthefuture,GeneralMotor'sremarkableconceptcar,theHy-wire.GMmayneveractuallyselltheHy-wiretothepublic,butitiscertainlyagoodillustrationofvariouswayscarsmightevolveinthenearfuture.
Hy-wireBasics
Twobasicelementslargelydictatecardesigntoday:
theinternalcombustionengineandmechanicalandhydrauliclinkages.
Ifyou'veeverlookedunderthehoodofacar,youknowaninternalcombustionenginerequiresalotofadditionalequipmenttofunctioncorrectly.Nomatterwhatelsetheydowithacar,designersalwayshavetomakeroomforthisequipment.
Thesamegoesformechanicalandhydrauliclinkages.Thebasicideaofthissystemisthatthedrivermaneuversthevariousactuatorsinthecar(thewheels,brakes,etc.)moreorlessdirectly,bymanipulatingdrivingcontrolsconnectedtothoseactuatorsbyshafts,gearsandhydraulics.Inarack-and-pinionsteeringsystem,forexample,turningthesteeringwheelrotatesashaftconnectedtoapiniongear,whichmovesarackgearconnectedtothecar'sfrontwheels.Inadditiontorestrictinghowthecarisbuilt,thelinkageconceptalsodictateshowwedrive:
Thesteeringwheel,pedalandgear-shiftsystemwerealldesignedaroundthelinkageidea.
ThedefiningcharacteristicoftheHy-wire(anditsconceptualpredecessor,theAUTOnomy)isthatitdoesn'thaveeitherofthesetwothings.Insteadofanengine,ithasafuelcellstack,whichpowersanelectricmotorconnectedtothewheels.Insteadofmechanicalandhydrauliclinkages,ithasadrivebywiresystem--acomputeractuallyoperatesthecomponentsthatmovethewheels,activatethebrakesandsoon,basedoninputfromanelectroniccontroller.Thisisthesamecontrolsystememployedinmodernfighterjetsaswellasmanycommercialplanes.
Theresultofthesetwosubstitutionsisaverydifferenttypeofcar--andaverydifferentdrivingexperience.Thereisnosteeringwheel,therearenopedalsandthereisnoenginecompartment.Infact,everypieceofequipmentthatactuallymovesthecaralongtheroadishousedinan11-inch-thick(28cm)aluminumchassis--alsoknownastheskateboard--atthebaseofthecar.Everythingabovethechassisisdedicatedsolelytodrivercontrolandpassengercomfort.
Thismeansthedriverandpassengersdon'thavetositbehindamassofmachinery.Instead,theHy-wirehasahugefrontwindshield,whichgiveseverybodyaclearviewoftheroad.Thefloorofthefiberglass-and-steelpassengercompartmentcanbetotallyflat,andit'seasytogiveeveryseatlotsoflegroom.Concentratingthebulkofthevehicleinthebottomsectionofthecaralsoimprovessafetybecauseitmakesthecarmuchlesslikelytotipover.
Butthecoolestthingaboutthisdesignisthatitletsyouremovetheentirepassengercompartmentandreplaceitwithadifferentone.Ifyouwanttoswitchfromavantoasportscar,youdon'tneedanentirelynewcar;youjustneedanewbody(whichisalotcheaper).
Youcanalwaysswitchbackwhenyouneedthevanagain.Thelogisticsofswitchingisstillunclear--iftheideacatcheson,theremightbespecialswitchingstationswhereyoucankeepyourdifferentcarbodies,ortheremightbeawayfordriverstoswitchthecarbodiesthemselvesintheirowngarage.
Power
The"Hy"inHy-wirestandsforhydrogen,thestandardfuelforafuelcellsystem.Likebatteries,fuelcellshaveanegativelychargedterminalandapositivelychargedterminalthatpropelelectricalchargethroughacircuitconnectedtoeachend.Theyarealsosimilartobatteriesinthattheygenerateelectricityfromachemicalreaction.Butunlikeabattery,youcancontinuallyrechargeafuelcellbyaddingchemicalfuel--inthiscase,hydrogenfromanonboardstoragetankandoxygenfromtheatmosphere.
Thebasicideaistouseacatalysttosplitahydrogenmolecule(H2)intotwoHprotons(H+,positivelychargedsinglehydrogenatoms)andtwoelectrons(e-).Oxygenonthecathode(positivelycharged)sideofthefuelcelldrawsH+ionsfromtheanodesidethroughaprotonexchangemembrane,butblockstheflowofelectrons.Theelectrons(whichhaveanegativecharge)areattractedtotheprotons(whichhaveapositivecharge)ontheothersideofthemembrane,buttheyhavetomovethroughtheelectricalcircuittogetthere.Themovingelectronsmakeuptheelectricalcurrentthatpowersthevariousloadsinthecircuit,suchasmotorsandthecomputersystem.Onthecathodesideofthecell,thehydrogen,oxygenandfreeelectronscombinetoformwater(H2O),thesystem'sonlyemissionproduct.(SeeHowFuelCellsWorkformoreinformation.)
Inahydrogenfuelcell,acatalystbreakshydrogenmoleculesintheanodeintoprotonsandelectrons.Theprotonsmovethroughtheexchangemembrane,towardtheoxygenonthecathodeside,andtheelectronsmaketheirwaythroughawirebetweentheanodeandcathode.Onthecathodeside,thehydrogenandoxygencombinetoformwater.Manycellsareconnectedinseriestomovesubstantialchargethroughacircuit.
Onefuelcellonlyputsoutalittlebitofpower,soyouneedtocombinemanycellsintoastacktogetmuchuseoutoftheprocess.Thefuel-cellstackintheHy-wireismadeupof200individualcellsconnectedinseries,whichcollectivelyprovide94kilowattsofcontinuouspowerand129kilowattsatpeakpower.Thecompactcellstack(it'saboutthesizeofaPCtower)iskeptcoolbyaconventionalradiatorsystemthat'spoweredbythefuelcellsthemselves.
ThissystemdeliversDCvoltagerangingfrom125to200volts,dependingontheloadinthecircuit.Themotorcontrollerbooststhisupto250to380voltsandconvertsittoACcurrenttodrivethethree-phaseelectricmotorthatrotatesthewheels(thisissimilartothesystemusedinconventionalelectriccars).
Theelectricmotor'sjobistoapplytorquetothefrontwheelaxletospinthetwofrontwheels.Thecontrolunitvariesthespeedofthecarbyincreasingordecreasingthepowerappliedtothemotor.Whenthecontrollerappliesmaximumpowerfromthefuel-cellstack,themotor'srotorspinsat12,000revolutionsperminute,deliveringatorqueof159pound-feet.Asingle-stageplanetarygear,witharatioof8.67:
1,stepsupthetorquetoapplyamaximumof1,375pound-feettoeachwheel.That'senoughtorquetomovethe4,200-pound(1,905-kg)car100milesperhour(161kph)onalevelroad.Smallerelectricmotorsmaneuverthewheelstosteerthecar,andelectricallycontrolledbrakecalipersbringthecartoastop.
Thegaseoushydrogenfuelneededtopowerthissystemisstoredinthreecylindricaltanks,weighingabout165pounds(75kilograms)total.Thetanksaremadeofaspecialcarboncompositematerialwiththehighstructuralstrengthneededtocontainhigh-pressurehydrogengas.Thetanksinthecurrentmodelholdabout4.5pounds(2kg)ofhydrogenatabout5,000poundspersquareinch(350bars).Infuturemodels,theHy-wireengineershopetoincreasethepressurethresholdto10,000poundspersquareinch(700bars),whichwouldboostthecar'sfuelcapacitytoextendthedrivingrange.
Ultimately,GMhopestogetthefuel-cellstack,motorsandhydrogen-storagetankssmallenoughthattheycanreducethechassisthicknessfrom11inchesto6inches(15cm).Thismorecompact"skateboard"wouldallowforevenmoreflexibilityinthebodydesign.
Control
TheHy-wire's"brain"isacentralcomputerhousedinthemiddleofthechassis.Itsendselectronicsignalstothemotorcontrolunittovarythespeed,thesteeringmechanismtomaneuverthecar,andthebrakingsystemtoslowthecardown.
Atthechassislevel,thecomputercontrolsallaspectsofdrivingandpoweruse.Butittakesitsordersfromahigherpower--namely,thedriverinthecarbody.Thecomputerconnectstothebody'selectronicsthroughasingleuniversaldockingport.ThiscentralportworksthesamebasicwayasaUSBportonapersonalcomputer:
Ittransmitsaconstantstreamofelectroniccommandsignalsfromthecarcontrollertothecentralcomputer,aswellasfeedbacksignalsfromthecomputertothecontroller.Additionally,itprovidestheelectricpowerneededtooperateallofthebody'sonboardelectronics.Tenphysicallinkageslockthebodytothechassisstructure.
Thedriver'scontrolunit,dubbedtheX-drive,isalotclosertoavideogamecontrollerthanaconventionalsteeringwheelandpedalarrangement.Thecontrollerhastwoergonomicgrips,positionedtotheleftandrightofasmallLCDmonitor.Tosteerthecar,youglidethegripsupanddownl
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