大運(yùn)輕卡驅(qū)動(dòng)橋的設(shè)計(jì)含開(kāi)題及CAD圖,大運(yùn)輕卡,驅(qū)動(dòng),設(shè)計(jì),開(kāi)題,CAD 309Chapter16Rear Axle AssemblyConstruction andOperationTechnical TermsSolid-axle rear suspensionIndependent rear suspensionDifferential drive gearsDrive pinion gearPinion bearingCollapsible spacerJam nutPinion shimRing gearWheel hopStandard differentialDifferential caseAfter studying this chapter,you will be able to:Explain the purpose of a rear axle assembly.Identify the major parts of a rear axle assembly.Describe the differential drive gears and related parts.Calculate rear axle ratio.Compare differential and rear axle assembly design variations.Describe the operation of a standard differential and of the various types of locking differentials.Spider gearsSide gearsLocking differentialLimited-slip differentialClutch-plate differentialCone differentialRatchet differentialTorsen differentialHydraulic locking differentialDifferential carrierAxle tubeRemovable carrierPinion pilot bearingSide bearingsIntegral carrierSolid drive axleAxle flangeAxle bearingAxle collarAxle retainer plateSemi-floating axleAxle shimFull-floating axleIndependently suspended drive axleThis sample chapter is for review purposes only.Copyright The Goodheart-Willcox Co.,Inc.All rights reserved.IntroductionThe rear axle assembly is used on rear-wheel drivevehicles.This assembly is the final leg of the drive train.Itis often called the final drive or rear end.The rear axleassembly is often mistakenly called the differential.Thedifferential is only part of the rear axle assembly.The basic design of rear axle assemblies has beenadopted by all manufacturers for many years.There areseveral variations,but all operate according to the samebasic principles.The major difference between rear axleassemblies depends on whether the vehicle has solid-axlerear suspension or independent rear suspension.Solid-axlerear suspension incorporates rigid and nonflexing driveaxles and axle tubes;both wheels move as one solid unitin response to bumps and potholes.Independent rearsuspension incorporates jointed drive axles(no axle tubes)that allow for flexibility and independent axle movement.This chapter is designed to identify and explain the con-struction and operation of various rear axle assemblies.Thematerial in this chapter provides a basis for understandinghow to properly troubleshoot and repair rear axle assemblies.Construction and Operation Overview The rear axle assembly includes the differentialassembly,the rear drive axles,and the rear axle housing.Rear axle assemblies are subjected to heavy loads from theengine and road.They are ruggedly constructed andseldom fail.The most common rear end failures are axlebearing failures.A typical rear axle assembly is shown inFigure 16-1.In a rear axle assembly,engine power enters the drivepinion gear from the drive shaft assembly and differentialpinion yoke/flange.The drive pinion gear,which is inmesh with the ring gear,causes the ring gear to turn.Theinteraction of the ring and drive pinion gears turns thepower flow at a 90 angle.The difference in the number ofteeth on the ring and pinion gears causes a reduction gearratio.This reduces turning speed,while increasing torque.Power from the ring gear flows through the differentialcase,spider gears,and side gears to the drive axles.Thedrive axles transfer power from the differential assembly tothe rear wheels.The bearings and rear axle housing are key com-ponents of the rear axle assembly.They are designed tosupport and align the differential assembly and the driveaxles.Notice that the bearings and axle housing are large,heavy-duty parts.This is to ensure they will stand up underhard usage.Seals and gaskets are also very important to theoperation of the rear axle assembly.Seals are used at thedifferential pinion yoke/flange and at the outer drive axles.Gaskets are used at housing interfaces,such as betweenthe differential cover and the housing,to provide a tightseal from the outside.Figure 16-2 is an exploded view of a common type ofrear axle assembly.Notice the relationship of the internalparts to the housing and to each other.Note that the rear310Manual Drive Trains and AxlesWheel,oraxle,bearingAxle sealAxleflangeSidebearingsDifferentialcaseInspection coverRing gearDrive axlePinionbearingsCompanionflangeDrivepinion gearPinion orspider gearsSide gearsRear axlehousingDriveaxleFigure 16-1.Most rear axle assemblies contain the same parts as shown in this cutaway.Note that some drive axles differ from thisbasic design.(Ford)Chapter 16Rear Axle Assembly Construction and Operation311BoltInspection coverThrustwasherSpidergearRetainingwasherSide gearThrust washerThrustwasherSidegearPinion shaftlock pinShimCupSidebearingPinionshaftSpidergearThrustwasherSidebearingCupShimDrivepinion gearRing and pinionassemblyPinionshimBoltBoltDifferential caseDifferentialcapPinionbearingPinionbearing cupBoltDifferentialcarrierRear axlehousingAxle tubeFiller plugBearingcupPinionspacerPinion bearingassemblyPinion sealPinion nutPinionflangeSlingerBoltAxlebearingSealNutDriveaxleRing gearBrake assemblyFigure 16-2.Exploded view of a rear axle assembly shown in Figure 16-1.(Ford)axle housing and drive axle designs will be different whenthe vehicle has independent rear suspension.Also,whenthe rear axle assembly is equipped with a limited-slipdifferential,it will contain more parts.These features willbe discussed later in this chapter.Differential AssemblyThe differential assembly in a rear-wheel drive vehiclehas three functions.The first,and most obvious,is toredirect the power flow to drive the rear wheels.Thepower flow must make a 90 turn between the drive shaftassembly and the rear wheels.This is accomplished in thedifferential assembly by the drive pinion and ring gears.The second function of the differential assembly isto multiply engine power,reducing speed at the outputin the process.If there were no gear reduction(1:1 gearratio),the vehicle would accelerate very slowly.In somecases,the engine would be unable to move the vehicle.At the very least,gas mileage would be harmed,sincethe engine would not reach its most efficient rpm range.For this reason,the ring and drive pinion assembly,bydesign,provides a reduced speed at its output.Thereduction is between 2:1 and about 5:1,depending onthe engine size,vehicle weight,and intended use of thevehicle.The third function of the differential assembly is toallow the vehicle to make turns.If the assembly did notmake allowances for the different speeds of the rear wheelsduring turns,one tire would lose traction with the groundas the vehicle turned corners.The differential assemblyallows the vehicle to make smooth turns.The differential assembly consists of numerous parts,including the differential drive gears(ring and drivepinion gears),pinion bearings,differential case,spiderand side gears,and side bearings.See Figure 16-3.Theseparts and their function are described in detail in thefollowing section.Differential Drive GearsThe differential drive gears also called the ring andpinion gearset,consist of the ring and drive pinion gears,Figure 16-4.These hypoid gears redirect power flow by90 and multiply engine power.The number of teeth in thering gear compared to the number of teeth in the drive pin-ion gear sets the rear axle ratio.For instance,if the ringgear has 40 teeth and the pinion gear has 10 teeth,theratio is 40:10,or 4:1.The ring gear always has more teeththan the drive pinion gear.Rear axle ratios can always bedetermined by dividing the number of teeth on the ringgear by the number of teeth on the drive pinion gear.Drive pinion gearThe drive pinion gear is a hardened-steel gear with anintegral shaft,Figure 16-5.It is machined to mesh with androtate the ring gear.The end of the shaft opposite the gearhas external splines that fit the internal splines of the differ-ential pinion yoke/flange.The gear is supported by twotapered roller bearings,called pinion bearings.By design,the axial centerline of the drive pinion gearlies below that of the ring gear.With this design,the piniongear is placed lower in the rear axle housing.This is doneto lower the drive shaft and,therefore,the drive shaft humpin the vehicle passenger compartment.The spiral design ofthe gear teeth allows the gears to mesh with a slidingmotion,creating a smooth power transfer.As a result of thesliding action,the gears must have a good supply of theproper lubricant.Gears of this type are called hypoid gears.312Manual Drive Trains and AxlesPinion bearingDrivepinion gearAdjustingnutSidebearingSide gearsRing gearSpidergearsDifferentialshaftCaseSide bearingAdjustingnutFigure 16-3.Relative positions of parts of a differential assembly.The interaction of the various parts of the differential may bemore easily understood by studying this illustration.(Subaru)Rear axlehousingPinionpreload shimDifferentialpinion yokePinionbearingsPinion depth shimDrivepinion gearRinggearSidebearingDifferentialcaseDifferentialbearing shims(endplay/preload)SidebearingFigure 16-4.The positions of the drive pinion gear and the ringgear are always about the same.The two pinion bearings andtwo side bearings are always tapered roller bearings that mustbe carefully adjusted.Some drive pinion gears have a thirdbearinga pinion pilot bearingfor support.Bearings andadjusting devices(shims or adjusting nuts)are usually locatedas shown.(DaimlerChrysler)The rear pinion bearing is pressed onto the drivepinion gear shaft at the gear end.The front pinion bearingis often a slip fit on the smaller end of the shaft.The outerraces,or bearing cups,of both bearings are pressed intothe rear axle housing.Either a solid spacer or a collapsible spacer(crushwasher)is used to set the pinion bearing preload.Thecollapsible spacer is designed to be slightly compressedwhen the drive pinion gear is installed in the rear axlehousing.The spacer maintains a mild pressure betweenthe front and rear pinion bearings,making it possible toaccurately adjust the bearing preload.The differential pinion yoke/flange has internalsplines that fit the external splines on the drive pinion gearshaft.See Figure 16-6.The rear of the yoke/flange,whereit fits into the rear axle housing,is machined smooth.Thisis the sealing surface for the pinion seal.The yoke/flange isheld to the drive pinion gear shaft by a large nut and washerthat threads onto the shaft.This nut is a type known as ajam nut.The top threads of the nut are deformed to tightlygrip the threads on the drive pinion gear shaft.This is aninterference fit.Tightening the nut also adjusts the pinionbearing preload.The pinion yoke is machined to accept the bearingcups of the rear universal joint.The cups are either pressedin and held with snap rings,or they are attached to theyoke with U-bolts or bolted-on straps.Pinion flanges are simply a two-piece yoke joined bymating flanges.The outer section has the yoke;the innersection has the external splines for the pinion gear shaft.These companion flanges,as they are also called,wouldbe separated at the flanged section to remove the driveshaft assembly,Figure 16-7.The position of the drive pinion gear relative to thering gear must be set exactly.Otherwise,the gears will benoisy and will wear out quickly.The position of the drivepinion gear in the housing must be carefully adjusted sothat it contacts the ring gear at exactly the right toothdepth.To make this adjustment to the ring and drive pinionclearance,a pinion shim is installed in the housing,behindthe rear bearing cup.The thickness of this shim determinesthe depth of the drive pinion gear in the housing.This shimis installed at the factory when the rear end is assembled.It must be checked for proper thickness whenever the drivepinion gear is removed.Figure 16-8 shows the position of the pinion shim onmost rear axle assemblies.This figure also shows the rela-tive position of the collapsible spacer.Ring gearThe ring gear,Figure 16-9,transfers power from thedrive pinion gear to the differential case.Both the ring gearand the case are machined to fit together tightly.Bolts areChapter 16Rear Axle Assembly Construction and Operation313Threads foryoke nutDrive pinionsplinesCollapsiblespacerDrive pinion gearRear pinionbearingDrive piniongear shaftFigure 16-5.A typical drive pinion gear.The rear pinion bear-ing is pressed on the drive pinion gear shaft.A collapsiblespacer is used to aid in pinion bearing installation.Threads andsplines at the front of the drive pinion gear shaft are used forinstalling the differential pinion yoke.(General Motors)Differentialpinion yokeDifferentialseal surfaceSplines lockgear to yokeDrivepinion gearDrive piniongear shaftFlat washerPiniongear nutHole forU-jointFigure 16-6.The differential pinion yoke slides over the drivepinion gear shaft and is secured by the pinion gear nut.Thetightening nut also preloads the pinion bearings.The outer sur-face of the drive pinion gear shaft seals against the front oil seal.U-jointRear axleassemblyCompanionflangesFlange boltsDrive shaftFigure 16-7.Some differential pinion yokes are two-pieceflanged assemblies,as shown here.This type of design isreferred to as a differential pinion flange,or companion flange.(Ford)used to hold the ring gear to the case.The bolts passthrough holes in the case and are threaded into tappedholes in the back of the ring gear.Since the ring and drive pinion gear teeth must meshaccurately to transmit motion without noise or damage,the position of the ring gear is important.Automotive tech-nicians should be familiar with gear terminology that willbe encountered while adjusting the differential assembly toobtain correct gear positions.The convex side,or driveside,and the concave side,or coast side,of the ring gearare pointed out in Figure 16-9A.These terms will be usedwhen differential gears are adjusted.The tooth parts thatmust be carefully adjusted are identified in Figure 16-9B.The terms heel and toe will be used extensively for ringand pinion gearset adjustment.Differential Case AssemblyWhen a vehicle makes a turn,the outer wheel travelsa greater distance than the inner wheelthe arc(orradius)of the turn is greater at the outer wheel.If the reardrive axles were simply connected together,both wheelswould have to travel an arc of the same length during aturn.Since this is impossible,one of the tires would losetraction,or slip,during the turn.If the tire did not slip,itwould skip over the road surface.This condition is calledwheel hop.The purpose of the differential case assembly is toallow the vehicle to make turns without slippage or wheelhop.It does this with an arrangement of gears that allowsthe rear wheels to turn at different speeds.Two basic typesof differential case assemblies used to accomplish this taskare the standard differential and the locking differential.Standard differentialThe standard differential,also called a single-pulldifferential,is composed of meshing spider and side gearsenclosed in a differential case.See Figure 16-10.The standard differential case is usually a one-pieceunit.The ring gear is bolted to the case.The case is usuallymade of cast iron.Occasionally,it is made of aluminum.Side bearings are usually pressed onto the case.The spider gears are made of hardened steel and areheld in place by a steel shaft called the pinion shaft.Thepinion shaft passes through the differential case and thecenter of the spider gears.It is attached to the case with abolt.Spider gears are also called pinion gears.Spider gears mesh with side gears,which are alsomade of hardened steel.When the ring gear and differen-tial case turn,the spider and side gears also turn.Powerflow is through the case,into the spider gears,and on intothe side gears.The side gears are splined to the drive axles.314Manual Drive Trains and AxlesRear U-jointFront pinionbearingPinionshimPiniongear nutDifferentialpinion yokeCollapsiblespacerRear pinionbearingFigure 16-8.Pinion shim and preload spacer locations.Properpinion adjustment is critical.The adjusting nut,preload spacer,and depth shim are all critical to proper pinion adjustment.(DaimlerChrysler)CorrectpatternToeConcave side(coast)Convex side(drive)HeelTop landProfileRootToeHeelLengthwisebearingarcABFigure 16-9.When installed,the ring gear is bolted to the differential case and meshes with the drive pinion gear.AThe ring gearhas convex and concave sides.The convex side is the drive side.It contacts the drive pinion gear when the vehicle is accelerating.The concave side is the coast side.It contacts the drive pinion gear when the vehicle is decelerating.BGear terminology will beimportant when the differential assembly is serviced.Proper heal and toe contact is critical to quiet operation and long life.(General Motors,DaimlerChrysler)They transfer power to the drive axles and rear wheels.Side gears are also called axle end gears.Some heavy-duty differentials contain four spidergears and two pinion shafts.In this design,there is a centerhole in one of the shafts.The other shaft passes through it.The side gears are splined to the drive axle.On somedifferentials,the side gears contain C-locks,which holdthe axles in place.See Figure 16-11.The spider and side gears are bevel gears.Powertransfer through the bevel gears causes them to be forcedaway from each other.This causes high thrust forces on thebacks of the gears,where they contact the differential case.Hardened-steel washers are usually installed between theback of the gears and the case.These washers provide asliding surface and reduce wear.See Figure 16-12.Figure 16-13 shows the operating states of the differ-ential while driving straight ahead and while drivingaround a corner.In Figure 16-13A,the vehicle is movingstraight ahead and both wheels are traveling at the samespeed.The spider and side gears rotate with the case butdo not move in relation to it.The entire case assemblyrotates as a unit.When the vehicle makes a turn,the axles and the sidegears begin turning at different speeds.The outer wheelthe left wheel,in the case of a right turnturns faster thanthe inner wheel,and the left side gear turns faster than theright side gear.See Figure 16-13B.As a result of thedifferent axle speeds,the spider gears begin to rotate.Theleft side gear,which is moving faster than the right sidegear,drives the spider gears,causing them to rotate on,orwalk around,the right side gear.Note that the differential case speed on turns is theaverage of the side gear speeds.This is because one sidegear is rotating faster than the case and the other side gearis rotating slower than the case.In Figure 16-14,when thevehicle makes a turn,the action of the differential allowsthe outer wheel to turn at 110%of case speed,while theinner wheel turns at 90%of differential case speed.Thesepercentages will vary with the radius of the turn.Locking differentialThe standard differential works well in most situa-tions.However,on very slippery surfaces,such as icy ormuddy roads,lack of traction can cause the rear wheels toslip.This is because the standard differential will drive thewheel with the least traction.If one drive wheel is on dry pavement and the otheris on ice or mud,the ring gear and differential case willdrive the spider gears.However,the spider gears will notdrive both side gears.When the spider gears are driven bythe differential case,they will walk around the side gearrelated to the wheel on dry pavement.As a result,thespider gears drive the slipping wheel,and the vehicle willnot move.The standard differential sends almost all enginepower to the slipping wheel.To overcome this problem,locking differentials areused.Locking differentials overcome traction problems bysending some power to both wheels,while allowing thevehicle to make normal turns.There are several differenttypes of locking differentials,including limited-slip,ratchet,and Torsen differentials.The two most common types of limited-slipdifferential are the clutch-plate differential and the conedifferential.The clutch-plate differential uses several fric-tion discs that look like small manual clutch discs.Thecone d