汽车手动变速箱外文翻译Word下载.docx
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汽车手动变速箱外文翻译Word下载.docx
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thetoothwidth.Ifthesegmentisinterruptedwherecrossingtheshaft,the
gearwheelisidle;
theoppositeoccursifthesegmentcrossesthelineofthe
shaftwithoutinterruption.Thenthewheelrotateswiththeshaft.Hubsare
representedaccordingtothesamerules,whilesleevesarerepresentedwitha
pairofhorizontalstrokes.Arrowsshowtheinputandoutputshafts.
Singlestagegearboxesareprimarilyappliedtofrontwheeldrivenvehicles,
becauseintheseitisusefulthattheinputandtheoutputshaftareoffset;
in
G.GentaandL.Morello,TheAutomotiveChassis,Volume1:
ComponentsDesign,425
MechanicalEngineeringSeries,
c_SpringerScience+BusinessMediaB.V.20094269.MANUALGEARBOXES
FIGURE9.1.Schemesforafourspeedgearboxshowninthreedifferentconfigurations:
a:
singlestage,b:
doublestageandc:
triplestage.
conventionalvehicles,ontheotherhand,itisbetterthatinputandoutputshafts
arealigned.
Thisiswhyrearwheeldrivenvehiclesusuallyadoptadoublestagegearbox.
Themulti-stageconfigurationissometimeadoptedonfrontwheeldriven
vehicleswithtransversalengine,becausethetransversallengthofthegearbox
canbeshortened;
itisusedwhenthenumberofspeedsorthewidthofthegears
donotallowasinglestagetransmissiontobeused.
Itshouldbenotedthatonafrontwheeldrivenvehiclewithtransversal
engine,havingdecidedonthevalueofthefronttrackandthesizeofthetire,
thelengthofthegearboxhasadirectimpactonthemaximumsteeringangleof
thewheelandthereforeontheminimumturningradius.
Thepositiveresultonthetransversaldimensionofmulti-stagegearboxesis
offsetbyhighermechanicallosses,duetotheincreasednumberofengagedgear
wheels.
Itshouldbenotedthatintriplestagegearboxes,showninthepicture,the
axesofthethreeshaftsdonotlieinthesameplane,astheschemeseemsto
show.Inalateralview,theoutlineofthethreeshaftsshouldberepresentedas
theverticesofatriangle;
thislay-outreducesthetransversaldimensionofthe
gearbox.Inthiscaseandothers,aswewillshowlater,thedrawingisrepresented
byturningtheplaneoftheinputshaftandofthecountershaftontheplaneof
thecountershaftandoftheoutputshaft.
Geartrainsusedinreversespeedareclassifiedseparately.Theinversionof
speedisachievedbyusinganadditionalgear.Asamatteroffact,inatrainof
threegears,theoutputspeedhasthesamedirectionastheinputspeed,while
theothertrainsoftwogearsonlyhaveanoutputspeedintheoppositedirection;
theaddedgearisusuallycalledidler.
ThemainconfigurationsarereportedinFig.9.2.
Inschemea,anaddedcountershaftshowsaslidingidler,whichcanmatch
twoclosegearsthatarenotincontact,as,forexample,theinputgearofthe
firstspeedandtheoutputgearofthesecondspeed.Itshouldbenotedthat,in
thisscheme,thedrawingdoesnotpreservetheactualdimensionoftheparts.9.1Manualgearboxclassification427
FIGURE9.2.Schemesusedforreversespeed;
suchschemesfiteverytypeofgearbox
lay-out.
Schemebshowsinsteadtwoslidingidlers,rotatingtogether;
thisarrange-
mentoffersadditionalfreedominobtainingagiventransmissionratio.Thecoun-
tershaftisoffsetfromthedrawingplane;
arrowsshowthegearwheelsthatmatch
whenthereversespeedisengaged.
Schemecissimilartoainrelationtotheidler;
itpairsanaddedspecific
wheelontheoutputshaftwithagearwheelcutontheshiftingsleeveofthefirst
andsecondspeed,whenitisinidleposition.
Configurationdshowsadedicatedpairofgears,withafixedidleranda
shiftingsleeve.
Thefollowingaretheadvantagesanddisadvantagesoftheconfigurations
showninthefigure.
•Schemesa,bandcaresimpler,butprecludetheapplicationofsynchro-
nizers(becausecouplesarenotalwaysengaged),nordotheyallowtheuse
ofhelicalgears(becausewheelsmustbeshiftedbysliding).
•Schemedismorecomplexbutcanincludeasynchronizerandcanadopt
helicalgears.
•Schemesa,bandcdonotincreasegearboxlength.4289.MANUALGEARBOXES
9.2MECHANICALEFFICIENCY
Themechanicalefficiencyofanautomotivegearwheeltransmissionishighcom-
paredtoothermechanismsperformingthesamefunction;
indeed,thevalueof
thisefficiencyshouldnotbeneglectedwhencalculatingdynamicperformance
andfuelconsumption.Thecontinuouseffortoftolimitfuelconsumptionjusti-
fiesthecareoftransmissiondesignersinreducingmechanicallosses.
Totaltransmissionlossesareconveyedupbytermsthatarebothdependent
andindependentoftheprocessedpower;
theprimarytermsare:
•Gearinglosses;
thesearegeneratedbyfrictionbetweenengagingteeth
(powerdependent)andbythefrictionofwheelsrotatinginairandoil
(powerindependent).
•Bearinglosses;
thesearegeneratedbytheextensionofthecontactareaof
rollingbodiesandbytheirdeformation(partlydependentonandpartly
independentofpower)andbytheirrotationintheairandoil(power
independent).
•Sealinglosses;
theyaregeneratedbyfrictionbetweensealsandrotating
shaftsandarepowerindependent.
•Lubricationlosses;
thesearegeneratedbythelubricationpump,ifpresent,
andarepowerindependent.
Alltheselossesdependontherotationalspeedofpartsincontactand,
therefore,onenginespeedandselectedtransmissionratio.
Table9.1reportsthevaluesofmechanicalefficiencytobeadoptedincalcu-
lationsconsideringwideopenthrottleconditions;
thesevaluesconsiderapairof
gearingwheelsoracompletetransmissionwithsplashlubrication;
inthesame
tablewecanseealsotheefficiencyofacompletepowershiftepicycloidalauto-
matictransmissionandasteelbeltcontinuouslyvariabletransmission.Forthe
twolasttransmissions,thetorqueconvertermustbeconsideredaslocked-up.
TABLE9.1.Mechanicalefficiencyofdifferenttransmissionmechanisms.
MechanismtypeEfficiency(%)
Completemanualgearbox
withsplashlubrication92–97
Completeautomatictransmission
(ep.gears)90–95
Completeautomaticgearbox
(steelbelt;
withoutpress.contr.)70–80
withpress.contr.)80–86
Pairofcyl.gears99.0–99.5
Pairofbevelgears90–939.2Mechanicalefficiency429
FIGURE9.3.Contributionstototalfrictionlossofasinglestagegearboxdesignedfor
300Nmasfunctionofinputspeed.
Itismorecorrecttoreferencepowerlossmeasurementasafunctionof
rotationalinputspeedratherthanefficiency.Figure9.3showstheexampleof
adoublestagetransmission,infourthspeed,atmaximumpower;
thedifferent
contributionstothetotalareshown.
Thiskindofmeasurementismadebydisassemblingthegearboxstepby
step,thuseliminatingtherelatedloss.
Inthefirststepallsynchronizerringsareremoved,leavingthesynchronizer
hubsonly;
mechanicallossesofnon-engagedsynchronizersare,therefore,mea-
surable.Thelossisduetotherelativespeedofnon-engagedlubricatedconical
surfaces;
thevalueofthislossdepends,obviously,onspeedandtheselected
transmissionratio.
Inthesecondstepallrotatingsealsareremoved.
Inthethirdstepthelubricationoilisremoved,andtherefore,thebulkof
thelubricationlossesiseliminated;
someoilmustremaininordertoleavethe
contactbetweenteethunaffected.
Byremovingthosegearwheelsnotinvolvedinpowertransmission,their
mechanicallossesarenowmeasurable.
Therestofthelossisduetobearings;
thepreviousremovalofpartscan
affectthisvalue.
Amoreexhaustiveapproachconsistsinmeasuringthecompleteefficiency
map;
theefficiencycanberepresentedasthethirdcoordinateofasurface,where
theothertwocoordinatesareinputspeedandenginetorque.Efficiencycalcu-
lationscanbemadebycomparinginputandoutputtorqueofaworkingtrans-
mission.
Suchmapcanshowhowefficiencyreachesanalmostconstantvalueata
modestvalueoftheinputtorque;
itmustnotbeforgottenthatstandardfuel
consumptionevaluationcyclesinvolvequitemodestvaluesoftorqueandthere-
foreimplyvaluesoftransmissionefficiencythatarechangingwithtorque.
Figure9.4showsaqualitativecrosssectionoftheaforesaidmap,cutat
constantenginespeed.Itshouldbenotedthatefficiencyisalsozeroatinput4309.MANUALGEARBOXES
FIGURE9.4.Mechanicalefficiencymap,asafunctionofinputtorqueatconstant
enginespeed;
thedottedlinerepresentsareasonableapproximationofthiscurve,tobe
usedonmathematicalmodelsforthepredictionofperformanceandfuelconsumption.
torquevaluesslightlygreaterthanzero;
asamatteroffact,frictionimpliesa
certainminimumvalueofinputtorque,belowwhichmotionisimpossible.
Agoodapproximationtorepresentmechanicalefficiencycanbemadeusing
thedottedbrokenlineasaninterpolationoftherealcurve.
9.3MANUALAUTOMOBILEGEARBOXES
9.3.1Adoptedschemes
Inm
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