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1、UNIT10THEDIFFERENTIALP99Mostcarshaveastandard,orunlimited-slip,differential.(Alimited-slipdifferentialcostsmoreandisnotnecessaryinmostnormaldrivingconditions.)Asmentioned,adifferentialmustsplitpowerunequallywhenacargoesaroundacorner.Likethetransmission,thedifferentialhasmanygearsandparts.10.1Th
2、eMainGearsSupposeashaftspinsinonedirection.Youwantthatshafttodriveanothershaftatanangleof90°tothefirstshaft.Youcandothisbymeshingtwogears,eachhavingteethsetata45°angle.Therewouldbeonegearoneachshaft.Together,thetwogearsproducea90°changeindirection.Figure10-1.Gearswithteethatsuchananglearecalled
3、bevelgearsbecausetheyarebeveled,orcutonanangle.ThebevelgearsinFigure10-1workwellwhenoneshaftmustdriveanother.Butinafinaldriveassembly,twoaxleshaftsmustbedriven.(Oneshaftgoestoeachdrivewheel.)Thenoneofthebeveledgearsmusthaveaholeinitscenterthroughwhichtheshaftextends.Thelargecirculargearontheaxl
4、eshaftsiscalledtheringgear.Figure10-1.Thefinaldriveassemblyalsoprovidesgearreductionsothatthedrivewheelsspinmoreslowlythanthedriveshaft.Thegearreductionvaries,dependingonenginesizeandpower,enginetorque,andvehiclesizeandweight.Ingeneralmostfinaldrivesproducegearreductionratiosofabout2.50:1to3.50
5、:1.Thus,thedrivewheelsturnataboutone-thirdthespeedofthedriveshaft.(Ifthedriveshaftspinsat3,000rpm,thedrivewheelsturnatabout1,000rpm.)Togivethenecessaryreduction,thedrivinggearinthefinaldrivemustbesmallerthanthedrivengear,whichistheringgear.Thus,thedrivinggearmustmakeseveralturnsforeverysingletu
6、rnoftheringgear.Thedrivinggeariscalledthepiniongearorpinion.Figure10-1.Thedriveshaftturnsthepinion.Thepinionrotatestheringgearandaxleshafts.Iftheteethofthebeveledgearsarecurved,thepinionmeshesmoreeasilyandquietlywiththelargerringgear.Nowwecanrefertothegearsasspiralbevelgears.Figure10-2showsaset
7、ofspiralbevelgears.10.2TheDifferentialSystemThefinaldriveworksfineaslongasbothdrivewheelsturnatthesamespeed.However,thissystemcannotprovidedifferentratesofspeedfordifferentwheels.Asnotedearlier,adifferentialsystemisneededtoallowfo
