汽车理论3动力性Automobile theory 3 dynamics.docx
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汽车理论3动力性Automobile theory 3 dynamics.docx
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汽车理论3动力性Automobiletheory3dynamics
汽车理论3动力性(Automobiletheory,3dynamics)
Thethirdchapterisabouttheselectionofenginepowerandthedeterminationoftransmissionratio
Learninggoal
Throughthestudyofthischapter,weneedtomasterthemethodofselectingenginepowerandgearnumberandtransmissionratio.
Thepowerandtransmissionoftheautomobileenginehaveagreatinfluenceonthepowerandfueleconomyoftheautomobile.Indeterminingtheseparameters,fullconsiderationmustbegiventomeetingthesetwobasicperformancerequirements.Inaddition,attentionshouldbepaidtodrivingrequirements.
3.1sectionenginepowerselection
Usuallyinthedesign,theenginepowerisinitiallyselectedfromthemaximumspeedrequiredtoensurethedesiredvehiclespeed.Althoughthemaximumspeedisonlyoneindicatorofpower,itessentiallyreflectstheaccelerationandclimbingabilityofthecar.Becausethehigherthemaximumspeed,thegreatertherequiredpoweroftheengine,thereservepowerofthecar,accelerationandclimbingcapacityisnecessarilybetter.
Ifthedesiredmaximumspeedisgiven,thepoweroftheselectedengineshallbenolessthanthesumoftheresistancepoweratthehighestspeed
(3-1)
Aftergiven,,and,afterthesevalues,youcanfindthevalueofthepower.
Inactualwork,wealsousetheexistingvehiclestatisticstoestimatethespecificpowerofthecartodeterminethespecificpowerofthecar.Thespecificpowerofthecaristhepoweroftheunitmassofthecar.ThecommonunitofthespecificpoweriskW/t,andthespecificpowerofthecarcanbeobtainedfromthefollowingformula:
Carspecificpower=(3-2)
Thevalueandvalueofvariousfreightcarsareapproximatelyequalandthemaximumspeedvarieslittle,butthetotalmassvariesgreatly.Themaximumspeedofthefreightcarisabout100km/h.Theaveragepowerofamediumtruckisabout10kW/t,thefirstofwhichisusedtoovercometherollingresistancepower(2/5),accountingforabout3-2ofthetotal.Forvarioustypesoffreightcars,thefirstitemhasapproximatelythesamevalue.Typesecondistoovercometheairresistancepowerpart,itchangeswiththetruck,totalqualityincreases,windwardareaincreaseislimited,soitemtwowillincreaseasthetotalmassdecreasesgradually.Therefore,thespecificpowerofdifferentfreightcarswillgraduallydecreasewiththeincreaseofitstotalmass.Thespecificpoweroffreightcarisgenerallymorethan7.35kW/t(10PS/t).Lightgoodsvehicleslessthan2~3Taremostlyvariantcarsofcars,whichhavebetterdynamicperformanceandlargerpower.Themaximumspeedofheavy-dutydumptruckislowandthespecificpowerissmaller.Therefore,thefreightcarcaninitiallyselectenginepoweraccordingtothesametotalmassandthespecificpowerstatisticsofthesametypeofvehicle.
Thecarspeedishigh,andthedynamicperformanceofdifferentcardifferencecanbelarge,moderncar'stopspeedisbetween140~200km/h;morepowerthanthedifference,thanthegeneralcarpowerbetween15~90kW/t.InGermany,theexpresswaydoesnotlimitthespeedofthecar,sothemaximumspeedofthecarishigher,between140and230km/h.
Manycountriesevenstipulatetheminimumspecificpowerofvehiclestoensurethatthepowerofvehiclesontheroadisnotlessthanacertainlevel,andthatsomepoorperformancevehiclesarepreventedfromimpedingtheflowofvehicles.
Thechoiceoftheminimumdriveratioofthe10.2drivetrain
Mostofthetime,thecarrunsatthetopgrade,thatis,thegearwiththeminimumgearratio.Therefore,theselectionoftheminimumgearratioisveryimportant.
Thetotaldriveratioofatransmissiontrainistheproductofthetransmissionratioofeachcomponentinthetransmissionsystem
Transmissionratiooftransmission;
Thetransmissionratioofthemainreducer;
-thetransmissionratioofaclutchorasecondarytransmission.
Theordinarycardoesnothaveaclutchorasecondarytransmission,andtheminimumtransmissionratioofthetransmissionisadirectoroverdrive.Whentheminimumtransmissionratioofdirecttransmission,minimumtransmissiontransmissionratioisthemainreducertransmissionratio;whentheminimumtransmissionratioforoverdrive,whiletheminimumtransmissiontransmissionratioshouldbeproductratiooftransmissionandthemainreducergearboxtopdrive.
Thefollowingfactorsshouldbeconsideredinselectingthetransmissionratioofthemainreducer:
3.2.1maximumspeed
Thetransmissionratioofthemainreducerisdifferent,thepositionoftheenginepowercurveisdifferentonthepowerbalancediagramoftheautomobile,andthemaximumspeeddeterminedbytheintersectionofthehorizontalroadresistancecurveandthepowercurveisdifferent.Whentheresistancepowercurvecoincideswiththeenginepowercurveatitsmaximumpowerpoint,themaximumspeedatthistimeisthemaximum,whichisthemaximumspeedoftheengine.Therefore,thetransmissionratioofthemainreducershouldbeselectedtothemaximumspeedofthecar,whichisequivalenttothemaximumpoweroftheenginewhenthemaximumspeedisthemaximum.
Reservepowerof3.2.2vehicles
Thetransmissionratioofthemainreducerisdifferent,andthereservepowerofthecarisdifferent.Thepowercurveoftheengineisshiftedtotheleft,thereservepowerofthevehicleisincreased,andthepowerperformanceisenhanced,butthefueleconomyispoor.Theenginepowercurveisshiftedtotheright,thereservepowerofthecarissmaller,buttheenginepowerutilizationrateishigh,andthefueleconomyisbetter.
3.2.
3drivingperformance
Theminimumdriveratioisalsoaffectedbythedrivingperformance.Thedrivingperformancereferstothetorqueresponse,noiseandvibrationofthepowerunit.Drivingperformanceisrelatedtosurge,acceleration,idlinginstability,tempering,knockingandshooting.Thefewerthesephenomena,thebetterdrivingperformance.Drivingperformanceisdeterminedbythedriverthroughsubjectiveevaluation.
Thefactorsthataffectthedrivingperformanceincludeenginedisplacement,cylindernumber,transmissionstiffnessandminimumdriveratioofpowertrain.Theminimumtransmissionratiohasagreaterinfluenceontorqueresponse.Iftheminimumdriveratioistoosmall,theenginewillworkunderheavyload,andtheaccelerationwillbepoor.Noiseandvibrationwilloccur.Iftheminimumtransmissionratioistoolarge,itwillmakethefueleconomyworse,theenginerunsathighspeed,thenoiseisalsorelativelylarge.
3.2.4fueleconomy
Whenchoosingtheminimumdriveratio,notonlythepower,butalsothefueleconomyshouldbeconsidered.Whentheminimumdriveratioischosen,itisusuallydone;inordertoensuresufficientreservepower,theminimumtransmissionratioisincreasedbyalittleless;inordertoincreasefueleconomyandminimizetheminimumtransmissionratio,theutilitymodelisslightlylarger.Accordingtostatistics,about60%ofthecarvalueisbetween0.9and1.1,between0.7and0.9isabout30%,andtherestabout10%isbetween1.1and1.39.
Theminimumtransmissionratiocanalsobedeterminedbythehighestpowerfactor.
Mediumgravityofthetotalmassofcar[N];
-thespeedofthecaratthetopoftheenginewhenthemaximumtorqueisdelivered.[/km/h].
Thegeneralrecommendationthemosthigh-endpowerfactor,mediumtruckis0.04~0.08,0.1~0.15=intermediatecar.
Selectionofthemaximumdriveratioofthe10.3drivetrain
Themaximumtransmissionratioofatransmissiontrainistheproductofthetransmissionratioofthetransmissiontothemainreduceratthetransmissiontothefirstgear.Determinethemaximumtransmissionratioofthedrivetrainistodeterminethetransmissionratioofthetransmissiontothemainreducer.
Whendeterminingthemaximumtransmissionratio,threemainfactorsareconsidered,namely,maximumclimbinggrade,adhesionconditionandminimumsteadyspeedofcar.
3.3.1maximumclimbinggrade
Whenthecarclimbs,thespeedislow,regardlessoftheairresistance,themaximumdrivingforceofthecarshouldbeabletoovercomethemaximumclimbingslope
Thatis
Igearratioshouldbe
Themaximumgradientingeneraltrucksisabout30%,whichis16.7degrees.Asedanshouldhavetheabilitytoclimbmorethan30%ramps.
3.3.2attachmentcondition
Afterdeterminingthemaximumdriveratio,itshallbeverifiedwhethertheadhesionconditionismet
Whenchecking,itisadvisablethattheadhesioncoefficientis=0.5to0.6.
3.3.3minimumsteadyspeed
Foroff-roadvehicletransmission,themaximumtransmissionratioshouldensurethatthecarcantravelsteadilyatverylowspeed.Thispreventsthesoilfrombeingimpactedbytheimpactandsheardamageonthesoftgroundanddamagethegroundadhesion.Maximumtransmissionratioshallbe
Minimumstablespeed.
Inaddition,themaximumtransmissionratioofthecarisdeterminedaccordingtotherequirementsoftheaccelerationcapacity,andcanbeselectedaccordingtothesameclassofcars.
10.4sectiontransmissiongearnumberandeachgeartransmissionratiochoice
Selectionofgearnumberin3.4.1drivesystem
Thereisacloserelationshipbetweenthepowerandfueleconomyofautomobileandthenumberofgearsintheautomobiletransmissionsystem.Theincreaseofthenumberofgearsmakestheenginemaximizethepowerandimprovestheaccelerationandclimbingabilityofthecar.Atthesametime,thenumberofstallsincreasesthepossibilitythattheenginewillworkinthelowfuelconsumptionareaandreducesthefuelconsumption.Asaresult,anincreaseinthenumberoftransmissiongearswillimprovethepowerandfueleconomyofthecar.
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- 汽车理论3动力性Automobile theory dynamics 汽车 理论 动力 Automobile