氢动力线控技术.docx

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