chapter 23 bennet
TRANSCRIPT
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Chapter 23
Heavy-Duty
Truck Axles
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Objectives (1 of 3)
Identify the types of axles used on trucks and
trailers.
Define the terms dead axle, live axle, pusher
axle, and tag axle.
Outline the construction of a drive axle carrier
assembly.
Explain how a pinion and crown gearsetchange the direction of powerflow.
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Objectives (2 of 3)
Describe differential action and list the
reasons it is required.
Identify the components required to create
differential action.
Describe the operation of the various drive
axle configurations.
Identify the components used in an interaxledifferential or power divider.
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Objectives (3 of 3)
Explain how an interaxle differential lock
functions.
Define the term spinout and explain how it is
caused.
Trace the powerflow path through different
types of differential carriers.
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Examples of Heavy-duty Axles
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Typical Steering Axle
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Trailer Axle
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Single Rear Drive Axle
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Cutaway Differential Carrier
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Shop Talk
Each OEM tends to use different words to describe the samecomponents, but in this text we will try to use the most commonterm.
A crown gear is also a ring gear, but we usually will use the firstterm.
An axle shaft also can be known as a half-shaft or drive shaft;once again, we usually will use the first term.
A drive shaft connects a drive wheel to a differential, whereas adriveshaft is a propeller shaft that delivers input torque to thefinal drive carrier. Confused? You bet, but, nevertheless, you
should try to become familiar with all the OEM terms so that youcan accurately interpret service literature.
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Typical Differential Components
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Differential Action
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Tandem Drive Axles
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Final Drive Axle Configurations
A single-reduction axle
A planetary double-reduction axle
A two-speed axle assembly
A tandem drive axle
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Bevel Gears
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Hypoid, Amboid,
and Spiral Bevel Gears
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Single-reduction Carrier
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Differential Lock
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Hypoid Double-reduction Carrier
Pl t
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Planetary
Double-reduction Gearing
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Forward Tandem Drive Axle
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Torque Distribution
with Power Divider Unlocked
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Torque Distribution
with Power Divider Locked
P Di id
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Power Divider
with External Lube Pump
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Disengaged Power Divider
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Torque Distribution
with Normal Traction Conditions
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Power Divider Engaged
T Di t ib ti
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Torque Distribution
When One Axle Loses Traction
D i A l Sh ft
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Drive Axle Shaft
Configurations
Two drive axle shaft configurations are used
to provide support between the axle hub and
the vehicle wheels.
Semi-floating axle shaft Full floating axle shaft
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Non-driving Axles
There are three categories of non-driving or
dead axles.
Steering axles
Lift and tag axles
Trailer axles
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Summary (1 of 6)
Axles can be divided into live axles and dead
axles.
Live axles are drive axles; they house the
gearing required to change the direction ofpowerflow and produce differential action.
Dead axles are designed to support chassis
loads. Dead axles include steering axles, tag
axles, pusher axles, and various types of
trailer axles.
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Summary (2 of 6)
The drive axles in trucks are known asdifferential carriers and are mounted in abanjo housing.
Driveshafts deliver driveline torque to thedifferential carrier that uses pinion and crowngearing to change the direction of powerflowand transmit it to the drive wheels.
Differential gearing is required in drive axlesand enables an outboard wheel to turn fasterthan an inboard wheel through a turn.
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Summary (3 of 6)
The critical differential components are a four
shaft spider with pinion gears on each shaft
that mesh to side gears on either side. The
side gears are splined to the axle shaftresponsible for driving the wheels.
During differential action, the slowdown of
one side gear is inversely proportional to the
increase in speed of its opposite side gear.
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Summary (4 of 6)
Most single-reduction axles are splash-
lubricated by gear oil as the geared
components rotate, but many differential
carriers with power dividers and multiple-reduction gearing use oil pumps to help
lubricate the assembly.
Tandem drive trucks require an inter-axle
differential or power divider to divide driveline
torque between the two drive axles.
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Summary (5 of 6)
In a tandem drive axle arrangement, differentialaction in the differential carriers and power divider
can cause spinout, in which a one-wheel spin can
produce fourfold velocities.
Most inter-axle differentials can be temporarily
locked out by a driver-activated switch.
This can help provide traction in slippery conditions
and reduce the potential for spinout.
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Summary (6 of 6)
Two-speed differential carrier gearing can beused on both single and tandem drive axlevehicles; control is by the driver.
A double-reduction differential carrier canproduce two ratio reductions. The firstreduction takes place at the crown and piniongearing, the second at a planetary gearset.
Torque proportioning power dividers reducespinouts by biasing torque transfer to thedrive axle with the most traction.