© 2012 Delmar, Cengage Learning Driveline Operation Chapter 75

© 2012 Delmar, Cengage Learning

Driveline Operation

Chapter 75


Objectives• Describe the operation of universal joints• Explain how a differential works• Understand the differences between types of

limited slip differentials• Describe the different types of rear axles and

bearings• Select the correct gear oil for different

applications


Objectives (cont’d.)• Identify differences between four-wheel-drive

types• Explain the parts and operation of a transfer case


Introduction• Driveline

– Parts that transfer power from transmission to rear wheels

• Driveshaft and universal joints• Axles and axle bearings• Differential

• Live axles – Turn with the wheels

• FWD vehicles – Have a transaxle with two halfshafts


Drive Shaft (RWD)• Typically include two universal joints and slip yoke


Slip Yoke• Attached to universal joint on front end of drive

shaft– Other end fits over splines on output shaft

• Slides in and out of transmission – As distance between transmission and

differential changes

• Automatic transmission– Sometimes a seal goes over the output shaft

• Keeps ATF from leaking out of slip yoke through its vent hole


Universal Joints• U-joints are located at ends of drive shaft

– Axle moves up or down: U-joint allows changes in angle at ends of drive shaft

• Cross and yoke– Most popular design

• Usually pressed fit into the yokes on drive shaft– Snap rings fit into grooves in the yoke

• Popular method of connecting to the differential– U-bolts hold U-joint centered between tabs in the

rear flange


Two-Piece Driveshaft• During factory balancing

– Weights spot-welded to drive shaft

– Vehicles with longer wheel base have a two-piece drive shaft

• Correctly assembled driveshaft – U-joint cups in alignment

• Improperly assembled: severely out of balance

• Center support bearing – Holds center of shaft where two shafts attach

– Sealed bearing is supported in rubber mount


Driveshaft Angle• Cardan U-joint operated at an angle

– Speed of driven shaft varies as it revolves

– Angle is increased: change in velocity increases

• Most manufacturers use angles less than three to four degrees with single U-joints

• One-piece drive shaft– U-joints arranged so they cancel each other

• Angles at each end of drive shaft – Must be almost equal or vibration results


Constant Velocity Joints• Vibration caused by drive shaft speed

– Canceled by putting two Cardan U-joints next to each other

• U-joints: connected by centering socket and yoke– Phased to cancel each other’s angle

– Speed change never leaves the joint

• CV joints: used on larger luxury vehicles and pickup trucks

• Ball and trunnion: used on FWD vehicles


Differential and Differential Construction

• Differential transfers power to wheels– Increases torque with final drive gear reduction

• Differential construction– Parts are housed in axle housing

– Pinion gear is splined to flange

• Crush sleeve functions– Keeps bearing separate from races

– Maintains preload on bearings

– Keeps front bearing race from spinning


Differential Housing• Differential housing holds drive pinion and case

– Banjo housing has removable pumpkin

– Salisbury axle (integral): third member not removable

• Top of housing has vent and breather tube– Breather tube usually runs into fender well

– Vent may have one-way check valve


Differential Operation• Each axle has splines

– Mesh with side gear splines

• Differential pinions mesh with side gears– Mounted on pinion shaft

• Spider gears – Side gears and differential pinions

• Power flow– During corner: side gears rotate against

differential pinions


Differential Gears• Hypoid gearset

– Pinion gear: lower than the centerline of ring gear

– Teeth of hypoid gear: curved in spiral shape

– Each tooth has concave and convex side• Convex side is the drive side• Concave side is the coast side



Gearsets• Ring and pinion gears: produced as matched set

– Ring and pinion gears marked • Assembled with marks facing each other

– Must be mounted together in exact position

• Gearset types– Hunting gearset: pinion gear tooth moves around

until it contacts all of the ring gear teeth

– Non-hunting gearset: one tooth on pinion gear meshes with same tooth on ring gear

– Partial non-hunting gearset: one pinion tooth contacts two to three different ring gear teeth


Axle Ratio and Limited Slip Differential

• Axel ratio: divide number of teeth on pinion gear into number of teeth on ring gear– Manual transmission has lower ratio

– Higher ratio produces better fuel economy

• Limited slip differential: locks up spider gears when one wheel loses traction– Puts traction on the still wheel

– Spider gears not locked during normal operation


Types of Limited Slip Differentials

• Several designs– Most popular has clutch packs

• Torque applied to clutch pack: side gear locks

– Older units: four pinion gears and two pinion shafts

– Cone-type: cones forced against case by springs

– Viscous coupling: sealed unit contains silicone fluid

– Detroit Locker differential: has a ratcheting pair of clutch packs that force it to lock up


Drive Axles and Bearings and Semi-Floating Axel Bearing Types

• Drive axles – Support weight of the car

• Semi-floating axle bearings– Bearing retained axle: bearing with inner race

pressed onto axle shaft• Retainer ring pressed onto axle shaft after bearing• Outside of bearing fits tightly into axle housing

– C-lock axle: bearing rides on hardened axel areas• Outer bearing race and rollers fit into axle housing• Axle bearing lubricated by oil mist


Independent Rear Suspension Axles

• Vehicle has independent rear suspension– Axles must pivot independently

• Two swing axles• Each axle has universal joint at one or both ends• Similar to those used in front-wheel-drive cars


Gear Oils• Special heavy liquid lubricant for gears and

bearings– Prevents high temperatures and scoring of parts

• Additives prevent corrosion and oxidation, reduce friction, limit wear, and prevent foaming– EP additives: cause formation of compounds

• API system– Classifies gear lubricants

• Limited slip gear oils– Require friction modifier additive


Four-Wheel Drive and Four-Wheel Drive Axle Assembly

• Types of four-wheel-drives– Operates like RWD with extra differential in front

– Operates like FWD with extra differential in rear

– All-wheel-drive are always in four-wheel-drive

• Axle assembly for four-wheel-drive: similar to two-wheel-drive rear axle– Drive shaft and universal joints transfer by way of

transfer case

– Ends of axle housing on front axles have to pivot to allow front wheels to be turned


Transfer Case• Allows for shifting between low and high range

and two-wheel and four-wheel drive• Power flow using gear drive transfer case

– 2H: through locked planetary gearset to mainshaft and rear differential

– 4H: input shaft to locked planetary gearset

– 4L: shifter moves clutch rearward

• Planetary low range– Planetary transfer case: ring gear pressed into

housing so it is held stationary


Locking Hubs• Allow four-wheel drive to be used in two-wheel

drive• Types

– Manual locking hubs: have on and off locks on front spindles

• Unlocked: front wheels not driven

– Automatic locking hubs: come on when vehicle shifted into four-wheel drive


All-Wheel Drive• Characteristics

– All four wheels driven

– Used to improve traction on icy or snowy driving

– Transfer engine power to wheel with most traction

– Lockout must be included when there is a center differential

– Viscous coupling allows front and rear wheels to revolve at different speeds

– Intelligent AWD flexibly distributes torque to wheels

Documents

© 2012 Delmar, Cengage Learning Driveline Operation Chapter 75