Differential and rear axle.ppt

Rear Axle Assembly Components
 Pinion drive gear
 Ring gear
 Differential case assembly
 Rear drive axles
 Rear axle bearings
 Axle housing

Rear Axle Power Flow
 The drive shaft turns the pinion gear
 The pinion gear turns the larger ring gear,
producing a gear reduction
 The ring gear is bolted to the differential case,
causing the case to rotate
 Small gears inside the case send torque to each axle

Rear Axle Functions
 Sends power from the drive shaft to the rear wheels
 Provides a final gear reduction
 Transfers torque through a 90º angle

Rear Axle Functions
 Splits the amount of torque going to each wheel
 Allows the wheels to rotate at different speeds in
turns
 Supports the rear axles, brake assemblies,
suspension components, and chassis

 The differential assembly uses drive shaft rotation
to transfer power to the axle shafts
 It must be capable of providing torque to both
axles, even when they are turning at different
speeds

Pinion Gear
 Turns the ring gear when the drive shaft is rotating
 The outer end is splined to the rear universal joint
companion flange or yoke
 The inner end meshes with the teeth on the ring
gear

Axle Housing
Note the pinion gear

Pinion Gear Bearings
 The pinion gear is supported with tapered roller
bearings
 The “gear preload” is a small amount of pressure
applied to the bearings to remove play and excess
clearance
 furnished by a crushable sleeve or shims

Pinion Gear Bearings
This pinion gear uses a pinion pilot bearing to help
support the gear

Ring Gear
 Driven by the pinion gear
 Transfers rotating power through an angle of 90º
 Contains more teeth than the pinion gear,
providing gear reduction
 Bolts to the differential case
 Gears are lapped together and timing marks are
applied at the factory for quiet operation

Differential Assembly
Note the ring gear

Hunting and Nonhunting Gears
 Hunting gearset
 does not mesh the same gear teeth during each
revolution of the ring gear
 Nonhunting gearset
 meshes the same gear teeth over and over during
gearset operation
 most common type
 markings must be aligned during assembly

Hypoid and
Spiral Bevel
Gears

Hypoid Gears
 The driving pinion centerline is offset, or lowered,
from the centerline of the ring gear
 Allow a lower hump in the vehicle floor
 Provide a larger gear tooth contact area, increasing
gear life and reducing noise

Spiral Bevel Gears
 The pinion and ring gears are on the same
centerline
 Used on early automobiles

Rear Axle Ratio
 Ratio of ring gear teeth to pinion gear teeth
 To calculate the ratio:
 count the number of teeth on each gear
 divide the number of ring gear teeth by the number
of pinion teeth

Rear Axle Ratio
 Ring gear has 30 teeth
 Pinion gear has 10 teeth
 What is the rear axle ratio?
# of ring gear teeth
# of pinion gear teeth
= 30
10
= 3, written 3:1

Rear Axle Ratio
 The average ratio is 3.50:1
 A high ratio, such as 4.11:1, provides better
acceleration, but less fuel economy
 A lower ratio, such as 3:1, reduces acceleration, but
increases fuel economy

Differential Carrier
 Provides a mounting place for the pinion gear,
differential case, and other components
 Two basic types are used:
 removable carrier
 integral carrier

Removable Carrier
Bolts to the front of the
axle housing
Integral Carrier
Constructed as part
of the axle housing

Differential Case
 Holds the ring gear, spider gears, and inner ends of
the axles
 Mounts and rotates in the carrier
 Supported by tapered roller bearings called case
bearings or carrier bearings

Differential Case

Spider Gears
 Mounted inside the case
 Small bevel gears
 Two axle gears or side gears
 splined to the axles
 Two pinion or idler gears
 ride on a pinion shaft that passes through the case

Differential Lubricant
 Usually SAE 80W90 gear oil
 Reduces friction between moving parts
 Ring gear rotation splashes the oil on the moving
parts
 Limited slip differentials may require special
lubricants

 The rear wheels do not always turn at the same
speed
 When turning or when tire diameters differ slightly,
the rear wheels must rotate at different speeds
 Differential action allows this speed difference

Driving Straight Ahead
 Both rear wheels turn at the same speed
 The rotating case and pinion shaft rotate the
differential pinion gears
 The pinion gears apply torque to the side gears and
axles
 The entire assembly rotates as one unit without any
pinion gear rotation on the pinion shaft

Driving Straight Ahead

Turning Corners
 The outer wheel is turning faster than the inner
wheel
 The outer wheel must travel farther (faster)
 The pinion gear rotation on the pinion shaft allows
each axle to change speed while still transferring
torque to propel the car

Turning Corners

 When one wheel of a conventional rear axle assembly
lacks traction, the other wheel will not propel the
vehicle
 Torque will flow to the axle that turns most easily
 Limited-slip differentials provide driving force to both
rear wheels at all times

Clutch Pack Differential
 Most popular limited slip design
 Uses a clutch pack
 Friction discs are sandwiched between steel plates
inside the differential case
 The friction discs are splined to the side gears
 The steel plates have tabs that lock into the case

A diaphragm spring preloads the
clutch discs

Operation (with Traction)
 Springs force the friction discs and steel plates
together
 Both rear axles try to turn with the case
 The vehicle can turn normally
 The clutch pack will slip

Operation (with Traction)

Operation
(with Wheel Spin)
 Under load, the rotation of the pinion gears pushes
out on the side gears, helping the springs apply the
clutch pack
 Friction in the clutch pack transfers torque from
the case to the side gears
 Both wheels get some torque output to improve
traction

Operation
(with Wheel Spin)

Cone Clutch Differential
 Uses the friction produced by the cone-shaped axle
gears to provide improved traction
 Springs force the cones against the ends of the case
 With the axles splined to the cone gears, the axles
tend to rotate with the case

Cone Clutch
Differential

Limited Slip Operation
 Under load, the pinion gears push outward on the
cone gears
 Friction between the cones and differential case
increases
 The drive wheels are turned with even greater
torque
 In turns, the side thrust on the axles helps release
one axle

Ratchet Differential
 Uses a series of cams and ramps to direct torque to
the drive axle with the most traction
 The operation is derived from relative wheel speed,
rather than traction
 The differential sends power through sets of teeth
that keep torque applied to the slowest turning axle

Operation
Straight ahead Left turn Right turn

Torsen Differential
 Uses complex worm gearsets
 The basic principle used is that worm gears can
drive other gears but cannot be driven
 Used in some exotic, high-priced production
vehicles

Torsen Differential

 Rear drive axles connect the differential side gears
to the drive wheels
 Most support the weight of the vehicle
 Often induction-hardened for increased strength
 Types include semifloating, three-quarter floating,
full-floating, and swing axles

Rear Drive Axle

Semifloating Axle
 Turns the drive wheel and supports the weight of
the vehicle
 Most common type of axle found on automobiles
 A ball or roller bearing fits between the axle shaft
and the axle housing
 Splines on the inner end fit into the differential side
gears

Semifloating Axle
Ball bearing type

Semifloating Axle
Roller bearing type, tapered end
accepts a wheel hub

Full-Floating Axle
Used on heavy-duty, pickup truck, and large truck
applications

Axle Retainer Plate
Used to keep the axle from sliding out
Rear axle seal prevents lubricant loss

Axle Shims
Used between the axle retainer plate and the housing
to limit axle end play

Swing Axles
 Used when the differential is rigidly mounted on
the car’s frame
 Universal joints at each end of the axle allow for up
and down suspension travel

Swing Axles

Differential Breather Tube
 Vents pressure or vacuum in or out of the rear axle
housing as temperature changes occur
 Without a breather tube, pressure could build as
the lubricant is warmed to operating temperature
 Lubricant could blow out the axle seals or pinion
seal

Front Drive Axle
 A front drive axle is similar to a rear drive axle;
however provisions must be made for steering the
front wheels
 The outer ends of the axles have universal joints
 The joints let the front wheels and hubs swivel
while transferring power

Front Drive Axle
Special hubs lock the drive axle to the hub and wheel
when in four-wheel drive

Front Drive Axle

Locking Hubs
 Transfer power from the driving axles to the driving
wheels
 Types:
 manual locking hub
 automatic locking hub
 full time hub

Hub Types
 Manual locking hub
 the driver must turn a latch on the hub to lock the
hub
 Automatic locking hub
 the hub locks the front wheels to axles when the
driver shifts into four-wheel drive
 Full time hub
 the front hubs are always locked and drive the front
wheels

Locking Hubs
 Manual and automatic locking hubs are most
common
 Enable the driveline to be in two-wheel drive for
use on dry pavement
 The front wheels can turn without turning the front
axles
 increases fuel economy
 reduces driveline wear

Differential and rear axle.ppt

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